Guidelines on the Production and Preservation of Digital Audio

Transcription

Guidelines on the Production and Preservation of Digital Audio Objects
International Association of Sound
and Audiovisual Archives
Internationale Vereinigung der
Schall- und audiovisuellen Archive
Association Internationale d’Archives
Sonores et Audiovisuelles
´ Internacional de Archivos
Asociacion
Sonoros y Audiovisuales
Technical Committee
Standards Recommended, Practices and Strategies
Guidelines on the Production
and Preservation of Digital
Audio Objects
IASA-TC04
Second Edition
IASA-TC04 Second Edition
http://www.iasa-web.org
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Asociacion
Technical Committee
Audio Objects
IASA-TC04
Second Edition
Edited by Kevin Bradley
Contributing authors
Kevin Bradley, National Library of Australia, President IASA and Vice Chair IASA TC;
Mike Casey, Indiana University; Stefano S. Cavaglieri, Fonoteca Nazionale Svizzera; Chris Clark, British Library (BL);
Matthew Davies, National Film and Sound Archive (NFSA); Jouni Frilander, Finnish Broadcasting Company;
Lars Gaustad, National Library of Norway and Chair IASA TC; Ian Gilmour, NFSA; Albrecht Häfner, Südwestrudfunk, Germany;
Franz Lechleitner, Phonogrammarchiv of the Austrian Academy of Sciences (OAW); Guy Maréchal, PROSIP;
Michel Merten, Memnon; Greg Moss, NFSA; Will Prentice, BL; Dietrich Schüller, OAW;
Lloyd Stickells and Nadia Wallaszkovits, OAW.
Reviewed by the IASA Technical Committee which included at the time
(in addition to those above)
Tommy Sjöberg, Folkmusikens Hus, Sweden; Bruce Gordon, Harvard University;
Bronwyn Officer, National Library of New Zealand;
Stig L. Molneryd, The National Archive of Recorded Sound and Moving Images, Sweden;
George Boston; Drago Kunej, Slovenian Academy of Sciences and Arts; Nigel Bewley, BL;
Jean-Marc Fontaine, Laboratoire d’Acoustique Musicale; Chris Lacinak; Gilles St. Laurent, Library and Archives, Canada;
and Xavier Sené, Bibliothèque Nationale de France.
© International Association of Sound and Audiovisual Archives (IASA) 2009
Translation not permissible without consent from IASA Executive Board
Published by the International Association of Sound and Audio Visual Archives
C/O Secretary-General:
Ilse Assmann
Media Libraries
South African Broadcasting Corporation
PO Box 931, 2006 Auckland Park
South Africa
1st Edition Published 2004
2nd Edition Published 2009
IASA TC-04 Guidelines in the Production and Preservation of Digital Audio Objects:
standards, recommended practices, and strategies: 2nd edition/ edited by Kevin Bradley
This publication provides guidance to audiovisual archivists on a professional approach
to the production and preservation of digital audio objects
Includes bibliographical references and index
ISBN 978-91-976192-2-6
1. Sound - Recording and reproducing - Digital techniques - Standards.
2. Sound recordings - Preservation - Standards. 3. Digital media - Preservation - Standards.
I. Kevin Bradley II. International Association of Sound and Audiovisual Archives (IASA) Technical Committee
Printed by Goanna Print
© International Association of Sound and Audio Visual Archives (IASA) 2009
Translation is not permitted without the consent of the IASA Executive Board and may only be undertaken
in accordance with the Guidelines & Policy Statement, Translation of Publications Guidelines,
Guidelines for the Translation of IASA Publications & Workflow for Translations
http://www.iasa-web.org/translation.asp
This publication is approved by the Sub-Committee on Technology
of the Memory of the World Programme of UNESCO
Contents
Preface to the Second Edition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Introduction to the First Edition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Chapter 1: Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Chapter 2: Key Digital Principles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Chapter 3: Metadata. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Chapter 4: Unique and Persistent Identifiers. . . . . . . . . . . . . . . . . . . . . . . . . . 28
Chapter 5: Signal Extraction from Original Carriers. . . . . . . . . . . . . . . . . . . . 31
Chapter 6: Preservation Target Formats and Systems . . . . . . . . . . . . . . . . . . 90
Chapter 7: Small Scale Approaches to Digital Storage Systems. . . . . . . . 118
Chapter 8: Optical discs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Chapter 9: Partnerships, Project Planning and Resources . . . . . . . . . . . . . 138
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Preface to the Second Edition
The process of debating the principles which underpin the work of sound preservation, and then discussing,
codifying and documenting the practices that we as professional sound archivists use and recommend, is to
necessarily identify the strengths and weaknesses in our everyday work. When the first version/edition of
TC-04 Guidelines in the Production and Preservation of Digital Audio Objects was completed and printed
in 2004 there was, in spite of our pride in that previous publication, little doubt amongst the IASA Technical
Committee that a second edition would be necessary to address those areas that we knew we would need
to be working on. In the intervening four years we as a committee have grown, extending our knowledge
and expertise in many areas, and helped to develop the standards and systems which implement sustainable
work and preservation practices. This second edition is the beneficiary of that work, and it contains much
that is vital in the evolving field of sustainable sound preservation by digital means.
Though we have incorporated much new information, and refined some of the fundamental chapters, the
advice provided in the second edition does not stand in opposition to that provided in the first. The IASATC 04 Guidelines in the Production and Preservation of Digital Audio Objects is informed by IASA-TC 03 The
Safeguarding of the Audio Heritage: Ethics, Principles and Preservation Strategy. A revised version of TC 03
was published in 2006 which took account of new developments in digital audio archiving, and of the much
more practical role of TC 04. TC 03 2006 concentrates on the principles and supersedes the earlier versions,
and these guidelines are the practical embodiment of the principles.
The major amendments in this second edition of TC 04 can be found in the chapters dealing with the
digital repositories and architectures. Chapter 3, Metadata, has been extensively enlarged and provides
significant and detailed advice on approaches to the management of data and metadata for the purposes of
preservation, reformatting, analysis, discovery and use. The chapter ranges widely across the subject area from
schemas through to structures to manage and exchange the content and considers the major building blocks
of data dictionaries, schemas, ontologies, and encodings. The sibling to this is Chapter 4, Unique and Persistent
identifiers, and it provides guidance on naming and numbering of files and digital works.
The new section included as Chapter 6 Preservation Target Formats and Systems, is structured around the
functional categories identified in the Reference Model for an Open Archival Information System (OAIS):
Ingest, Archival Storage, Preservation Planning, Administration and Data Management, and Access, and each
of the subsequent Sections deals with each subject area. The use of this conceptual model in organising the
book has two important consequences: Firstly, it uses the same functional categories as the architectural
design of the major repository and data management systems, which means it has real world relevance.
Secondly, identifying separate and abstracted components of a digital preservation strategy allows the
archivist to make decisions about various parts of the process, rather than trying to solve and implement
the monolithic whole. Chapter 9, Partnerships, Project Planning and Resources, is an entirely new chapter,
and provides advice on the issues to consider if a collection manager decides to outsource all or part of the
processes involved in the preservation of the audio collections.
Chapter 7, Small Scale Approaches to Digital Storage Systems, considers how to build a low cost digital
management system which, while limited in scope, still adheres to the principles and quality measures identified
in chapter 6.
Chapter 8 revisits the risks associated with optical disc storage and makes recommendations as to their
management, while suggesting the advice in chapters 6 and 7 may be more useful in the long term management
of digital content.
2
Preface to the Second Edition
Chapter 5, Signal Extraction from Original Carriers, was one of the most practical and informed components
of the first edition, and it remains a source of practical knowledge, and information on standards and advice.
As part of the review process the chapters on signal extraction have been refined, and extra useful advice
has been added. An extra section, 5.7 Field Recording Technologies and Archival Approaches, has been
added, and it addresses the question of how to create a sound recording in the field for which the content is
intended for long term archival storage.
Chapter 2, Key Digital Principles, adheres to the same standards expressed in the earlier edition. There is,
however, more explanatory detail, and technical information, particularly regarding the digital conversion
processes, has been provided in more precise and standard language.
TC 04 represents a considerable effort and commitment from the IASA Technical Committee, not only
those who created the original text, but also those who reviewed and analysed the chapters until we
reached a satisfactory explanation. To my friends and colleagues in the TC goes my respect for the detailed
knowledge and gratitude for their generosity in sharing it. The quality of this new edition is a testament to
their expertise.
Kevin Bradley
Editor
November 2008
3
Introduction to the First Edition
Digital audio has, over the past few years, reached a level of development that makes it both effective and
affordable for use in the preservation of audio collections of every magnitude. The integration of audio
into data systems, the development of appropriate standards, and the wide acceptance of digital audio
delivery mechanisms have replaced all other media to such an extent that there is little choice for sound
preservation except digital storage approaches. Digital technology offers the potential to provide an
approach that addresses many of the concerns of the archiving community through lossless cloning of audio
data through time. However, the processes of converting analogue audio to digital, transferring to storage
systems, of managing and maintaining the audio data, providing access and ensuring the integrity of the
stored information, present a new range of risks that must be managed to ensure that the benefits of digital
preservation and archiving are realised. Failure to manage these risks appropriately may result in significant
loss of data, value and even audio content.
This publication of the Technical Committee of the International Association of Sound and Audiovisual
Archives (IASA) “Guidelines on the Production and Preservation of Digital Audio Objects” is intended to
provide guidance to audiovisual archivists on a professional approach to the production and preservation
of digital audio objects. It is the practical outcome of the previous IASA Technical Committee paper, IASATC 03; “The Safeguarding of the Audio Heritage: Ethics, Principles and Preservation Strategy, Version 2,
September 2001”. The Guidelines addresses the production of digital copies from analogue originals for
the purposes of preservation, the transfer of digital originals to storage systems, as well as the recording of
original material in digital form intended for long-term archival storage. Any process of digitisation is selective,
the audio content itself supplies more information to potential users than is contained in the intended signal
and the standards of analogue to digital conversion fix the limits of the resolution of the audio permanently
and, unless carefully undertaken, partially.
There are three main parts to the content of the Guidelines:
• Standards, Principles and Metadata
• Signal Extraction from Originals
• Target Formats
Standards, Principles and Metadata: Of the four basic tasks that are performed by all archives — acquisition,
documentation, access, preservation, the primary task is to preserve the information placed in the care of
the collection (IASA-TC 03, 2001). However, if the tasks of acquisition and documentation are undertaken in
combination with a well planned digital preservation strategy that adheres to adequate standards, the task of
providing access is facilitated by the process. Long term access is a product of appropriate preservation.
Adherence to widely used and accepted standards suitable for the preservation of digital audio is a
fundamental necessity of audio preservation. The IASA Guidelines recommend linear PCM (pulse code
modulation) (interleaved for stereo) in a .wav or preferably BWF .wav file (EBU Tech 3285) for all two track
audio. The use of any perceptual coding (“lossy compression”) is strongly discouraged. It is recommended
that all audio be digitised at 48 kHz or higher, and with a bit depth of at least 24 bit. Analogue to Digital
(A/D) conversion is a precision process, and low cost converters integrated into computer sound cards
cannot meet the demands of archival preservation programs.
Once encoded as a data file, the preservation of the audio faces many of the same issues as those of all
digital data, and foremost in managing these is the assigning of a unique Persistent Identifier (PI) and providing
appropriate metadata. Metadata is not just the descriptive information that allows the user or archive to
identify the content, but also includes the technical information that enables the recognition and replaying
4
Introduction to the First Edition
of the audio, and the preservation metadata that retains information about the processes that went to
generate the audio file. It is only thus that the integrity of the audio content can be guaranteed. The digital
archive will depend on comprehensive metadata to maintain its collection. A well planned digital archive will
automate the production of much of the metadata and should include the original carrier, its format and
state of preservation, replay equipment and parameters, the digital resolution, format, all equipment used, the
operators involved in the process and any processes or procedures undertaken.
Signal Extraction from Originals: “Sound archives have to ensure that, in the replay process, the recorded
signals can be retrieved to the same, or a better, fidelity standard as was possible when they were
recorded… (also) carriers are the bearers of information: desired or primary information, consisting of the
intended sonic content, and ancillary or secondary information which may take manifold forms. Both primary
and secondary information form part of the Audio Heritage.” (IASA-TC 03, 2001).
To take full advantage of the potential offered by digital audio it is necessary to adhere to the above
principles and ensure that the replay of the audio original is made with a full awareness of all the possible
issues. This requires knowledge of the historic audio technologies and a technical awareness of the advances
in replay technology. Where appropriate, the Guidelines provide advice on the replay of historical mechanical
and other obsolete formats, including, cylinders and coarse groove discs, steel wire and office dictation
systems, vinyl LP records, analogue magnetic tape, cassette and reel, magnetic digital carriers such as DAT
and its video tape based predecessors, and optical disk media such as CD and DVD. For each of the formats
there is advice on selection of best copy, cleaning, carrier restoration, replay equipment, speed and replay
equalisation, corrections for errors caused by misaligned recording equipment and removal of storage related
signal artefacts and the time required to undertake a transfer to digital. All of these are important topics
which are addressed in the Guidelines with a consideration of the associated ethical issues, though the latter
issue is particularly significant as many digitisation plans fail to budget for the considerable time constraints of
an audio transfer process.
All the parameters mentioned above must be determined objectively, and appropriate records kept of every
process. Digital storage and associated technologies and standards enable an ethical approach to sound
archiving by enabling the production of documentation and its storage in linked, related metadata fields.
Target Formats: Data can be stored in many ways and on many carriers and the appropriate type of
technology will be dependant on the circumstances of the institution and its collection. The Guidelines
provide advice and information on various suitable approaches and technologies including Digital Mass
Storage Systems (DMSS) and small scale manual approaches to digital storage systems, data tape, hard disks,
optical disks including CD and DVD recordable and magneto optical disks (MO).
No target format is a permanent solution to the issue of digital audio preservation, and no technological
development will ever provide the ultimate solution; rather they are a step in a process whereby institutions
will be responsible for maintaining data through technological changes and developments, migrating
data from the current system to next for as long as the data remains valuable. The DMSS with suitable
management software are the most appropriate for the long term maintenance of audio data. “Such systems
permit automatic checking of data integrity, refreshment, and, finally, migration with a minimum use of human
resources” (IASA-TC 03, 2001). These systems can be scaled to suit smaller archives, though this will most
often result in an increased responsibility for manual data checking. Discrete storage formats such as CD
and DVD recordable, and magneto optical disks (MO) are inherently less reliable. The Guidelines suggest
standards and approaches to maintaining the data on these carriers, while recommending that the more
reliable solutions found in integrated storage systems are to be substantially preferred.
5
Chapter 1: Background
1.1
Audiovisual archives hold a responsibility for the preservation of cultural heritage covering all
spheres of musical, artistic, sacred, scientific, linguistic and communications activity, reflecting
public and private life, and the natural environment, held as published and un-published
recorded sound and image.
1.2
The aim of preservation is to provide our successors and their clients with as much of the
information contained in our holdings as it is possible to achieve in our professional working
environment. It is the responsibility of an archive to assess the needs of its users, both current and
future, and to balance those needs against the conditions and resources of the archive. The ultimate
purpose of preservation is to ensure that access to the audio content of collection is available to
approved users, current and future, without undue threat or damage to the audio item.
1.3
As the lifespan of all audio carriers is limited by their physical and chemical stability, as well as the
availability of the reproduction technology and, as the reproduction technology itself may be a
potential source of damage for many audio carriers, audio preservation has always required the
production of copies that can stand for the original as preservation duplicates, which in the parlance
of digital archiving have come to be known as “preservation surrogates”. The need to migrate
content to another storage system applies to carriers of digital audio originals perhaps even more
so as they may be endangered by the ever shorter lifetimes of highly sophisticated hardware and
related software in the market, which, sometimes only a few years after their market introduction,
will lead to the total obsolescence of replay equipment. However, the same constraints that apply to
the original item will wholly, or in part, apply to the preservation target format, requiring continued
reduplication. If preservation had continued by serial duplication in the analogue domain this would
have produced a degradation of the audio signal with each subsequent generation.
1.4
The potential offered by the production of digital surrogates for the purpose of preservation
seems to provide an answer to linked issues of preservation and access. However, the decisions
made about digital formats, resolutions, carriers and technology systems will impose limits on
the effectiveness of digital preservation that cannot be reversed, as will the quality of audio being
encoded. Optimal signal extraction from original carriers is the indispensable starting point of each
digitisation process. As recording media very often requires very specific replay technology, timely
organisation of copying into the digital domain must take place, before obsolescence of hardware
becomes critical.
1.5
The ability to recopy the captured digital copy without further loss or degradation has often led
enthusiastic archivists to describe it as “eternal preservation”. The easy production of low bit-rate
distribution copies broadens the ability of archives to provide access to their collections without
endangering the original item. However, far from being eternal, poorly managed digital archiving
practices may lead to a reduction in the effective lifespan and integrity of audio content, whereas a
well managed digital conversion and preservation strategy will facilitate the realisation of the benefits
promised by digital technology. Similarly, a poorly planned system requiring manual intervention may
present a management task of considerable dimension that could be beyond the capabilities of the
collection managers and curators and so endanger the collection. A well planned system should
enable automation of the processes and so preservation can proceed in a timely manner. No system
for preserving sound will provide a one-off solution; any preservation solution will require future
transfers and migrations that must be planned for when the material is first digitised and stored.
6
Background
1.6
The Guidelines address audio carriers such as cylinders and coarse groove discs, steel wire and
office dictation systems, vinyl LP records, analogue magnetic tape, cassette and reel, magnetic digital
carriers such as DAT and its video tape based predecessors, and optical disk media such as CD
and DVD. Though many of the principles contained herein will be applicable, sound for film is not
specifically addressed. This document does not consider piano rolls, MIDI files or other systems
which are player directions rather than encoded audio. The following principles outline the areas in
which critical decisions must be made in the transfer to and management of digital audio materials.
7
Chapter 2: Key Digital Principles
2.1
Standards: It is integral to the preservation of audio that the formats, resolutions, carrier and
technology systems selected adhere to internationally agreed standards appropriate to the intended
archival purposes. Non-standard formats, resolutions and versions may not in the future be included
in the preservation pathways that will enable long term access and future format migration.
2.2
Sampling Rate: The sampling rate fixes the maximum limit on frequency response. When producing
digital copies of analogue material IASA recommends a minimum sampling rate of 48 kHz for any
material. However, higher sampling rates are readily available and may be advantageous for many
content types. Although the higher sampling rates encode audio outside of the human hearing range,
the net effect of higher sampling rate and conversion technology improves the audio quality within
the ideal range of human hearing. The unintended and undesirable artefacts in a recording are also
part of the sound document, whether they were inherent in the manufacture of the recording or
have been subsequently added to the original signal by wear, mishandling or poor storage. Both must
be preserved with utmost accuracy. For certain signals and some types of noise, sampling rates in
excess of 48 kHz may be advantageous. IASA recommends 96 kHz as a higher sampling rate, though
this is intended only as a guide, not an upper limit; however, for most general audio materials the
sampling rates described should be adequate. For audio digital-original items, the sampling rate of
the storage technology should equal that of the original item.
2.3
Bit Depth: The bit depth fixes the dynamic range of an encoded audio event or item. 24 bit audio
theoretically encodes a dynamic range that approaches physical limits of listening, though in reality
the technical limits of the system is slightly less. 16 bit audio, the CD standard, may be inadequate
to capture the dynamic range of many types of material, especially where high level transients are
encoded such as the transfer of damaged discs. IASA recommends an encoding rate of at least 24
bit to capture all analogue materials. For audio digital-original items, the bit depth of the storage
technology should at least equal that of the original item. It is important that care is taken in
recording to ensure that the transfer process takes advantage of the full dynamic range.
2.4
Analogue to Digital Converters (A/D)
2.4.1
In converting analogue audio to a digital data stream, the A/D should not colour the audio or add
any extra noise. It is the most critical component in the digital preservation pathway. In practice, the
A/D converter incorporated in a computer’s sound card can not meet the specifications required
due to low cost circuitry and the inherent electrical noise in a computer. IASA recommends the use
of discrete (stand alone) A/D converters connected via an AES/EBU or S/PDIF interface, IEEE1394
bus-connected (firewire) discrete A/D converters or USB serial interface-connected discrete
A/D converters that will convert audio from analogue to digital in accordance with the following
specification. All specifications are measured at the digital output of the A/D converter, and are
in accordance with Audio Engineering Society standard AES 17-1998 (r2004), IEC 61606-3, and
associated standards as identified.
2.4.1.1 Total Harmonic Distortion + Noise (THD+N)
With signal 997 Hz at -1 dB FS, the A/D converter THD+N will be less than -105 dB unweighted,
-107 dB A-weighted, 20 Hz to 20 kHz bandwidth limited.
With signal 997 Hz at -20 dB FS, the A/D converter THD+N will be less than -95 dB unweighted,
-97 dB A-weighted, 20 Hz to 20 kHz bandwidth limited.
8
Key Digital Principles
2.4.1.2. Dynamic Range (Signal to Noise)
The A/D converter will have a dynamic range of not less than 115 dB unweighted, 117 dB
A-weighted. (Measured as THD+N relative to 0 dB FS, bandwidth limited 20 Hz to 20 kHz,
stimulus signal 997 Hz at -60 dB FS).
2.4.1.3. Frequency Response
For an A/D sampling frequency of 48 kHz, the measured frequency response will be better
than ± 0.1 dB for the range 20 Hz to 20 kHz.
For an A/D sampling frequency of 96 kHz, the measured frequency response will be better
than ± 0.1 dB for the range 20Hz to 20 kHz, and ± 0.3 dB for the range 20 kHz to 40 kHz.
For an A/D sampling frequency of 192 kHz, the frequency response will be better than
± 0.1 dB for the range 20Hz to 20 kHz, and ± 0.3 dB from 20 kHz to 50 kHz (reference
audio signal = 997 Hz, amplitude -20 dB FS).
2.4.1.4 Intermodulation Distortion IMD (SMPTE/DIN/AES17)
The A/D converter IMD will not exceed -90 dB. (AES17/SMPTE/DIN twin-tone test
sequences, combined tones equivalent to a single sine wave at full scale amplitude).
2.4.1.5 Amplitude Linearity
The A/D converter will exhibit amplitude gain linearity of ± 0.5 dB within the range -120
dB FS to 0 dB FS. (997 Hz sinusoidal stimuli).
2.4.1.6 Spurious Aharmonic Signals
Better than -130 dB FS with stimulus signal 997 Hz at -1 dBFS
2.4.1.7 Internal Sample Clock Accuracy
For an A/D converter synchronised to its internal sample clock, frequency accuracy of the
clock measured at the digital stream output will be better than ±25 ppm.
2.4.1.8 Jitter
Interface jitter measured at A/D output <5ns.
2.4.1.9 External Synchronisation
Where the A/D converter sample clock will be synchronised to an external reference
signal, the A/D converter must react transparently to incoming sample rate variations ±
0.2% of the nominal sample rate. The external synchronistation circuit must reject incoming
jitter so that the synchronised sample rate clock is free from artefacts and disturbances.
2.4.2
IEE1394 and USB Audio Interfaces. Many A/D converters now provide the facilities to directly
interface to a host computer via the high speed IEEE1394 (firewire) and USB 2.0 serial interfaces.
Both systems are successfully implemented as audio transmission interfaces across the major
personal computer platforms, and can reduce the requirement to install a specialised, high-quality
soundcard interface in the computer chassis. Audio quality is generally independent of the bus
technology in use.
2.4.3
Selection of A/D Converters: The A/D converter is the most critical piece of technology in the
digital preservation pathway. When choosing a convertor, and before any further evaluation is
undertaken, IASA recommends that all specifications are tested against the reference standards
described above. Any converter which does not meet the basic IASA technical specifications will
produce less than accurate conversions. In conjunction with technical evaluation, statistically valid
blind listening tests should be carried out on short listed converters to determine overall suitability
and performance. All the specifications and testing described above are stringent and complex,
9
and these specifications are highly important in selecting and evaluating analogue to digital
convertors. The published specifications from the equipment manufacturers are sometimes
challenging to compare, often incomplete and occasionally difficult to reconcile with the
performance of the device they purport to represent. It may suit certain communities or groups to
undertake group or panel testing to maximise resources. Certain institutions, such as state archives,
libraries or academic science departments may be in a position to assist with testing.
2.5
Sound Cards: The sound card used in a computer for the purposes of audio preservation should
have a reliable digital input with a high quality digital audio stream synchronisation mechanism,
and pass a digital audio data stream without change or alteration. As a discrete (stand alone) A/D
converter must be used, the primary purpose of a sound card in audio preservation is in passing a
digital signal to the computer data bus, though it may also be used for returning the converted signal
to analogue for monitoring purposes. Care should be taken in choosing a card that accepts the
appropriate sampling and bit rates, and does not inject noise or other extraneous artefacts. IASA
recommends the use of a high quality sound card that meets the following specification:
2.5.1
2.5.2
2.5.3
2.5.4
2.5.5
2.5.6
2.5.7
2.5.8
Sample rate support: 32 kHz to 192 kHz +/- 5%.
Digital audio quantisation: 16-24 bits.
Varispeed: automatic by incoming audio or wordclock.
Synchronisation: internal clock, wordclock, digital audio input.
Audio interface: high speed AES/EBU conforming to AES3 specifications.
Jitter acceptance and signal recovery on inputs up to 100ns without error.
Digital audio subcode pass-through.
Optional timecode inputs.
2.6
Computer Based Systems and Processing Software: Recent generations of computers have
sufficient power to manipulate large audio files. Once in the digital domain, the integrity of the
audio files should be maintained. As noted above the critical points in the preservation process
are converting the analogue audio to digital (which relies on the A/D converter), and entering the
data into the system, either through the sound card or other data port. However, some systems
truncate the word length of an item in order to process it, resulting in a lower effective bit rate and
others may only process compressed file formats, such as MP3, neither of which is acceptable. IASA
recommends that a professional audio computer based system be used whose processing word
length exceeds that of the file (i.e. greater than 24 bit) and which does not alter the file format.
2.7
Data Reduction: It has become generally accepted in audio archiving that when selecting a digital
target format, formats employing data reduction (frequently mistakenly called data “compression”)
based on perceptual coding (lossy codecs) must not be used. Transfers employing such data
reduction mean that parts of the primary information are irretrievably lost. The results of such
data reduction may sound identical or very similar to the unreduced (linear) signal, at least for the
first generation, but the further use of the data reduced signal will be severely restricted and its
archival integrity has been compromised.
2.8
File Formats
2.8.1
There are a number of linear audio file formats that may be used to encode audio, however, the
wider the acceptance and use of the format in a professional audio environment, the greater the
likelihood of long term acceptance of the format, and the greater the probability of professional
tools being developed to migrate the format to future file formats when that becomes necessary.
10
Because of the simplicity and ubiquity of linear Pulse Code Modulation (PCM) [interleaved for
stereo] IASA recommends the use of WAVE, (file extension .wav) developed by Microsoft and IBM
as an extension from the Resource Interchange File Format (RIFF). Wave files are widely used in the
professional audio industry.
2.8.2
BWF .wav files [EBU Tech 3285] are an extension of .wav and are supported by most recent
audio technology. The benefit of BWF for both archiving and production uses is that metadata can
be incorporated into the headers which are part of the file. In most basic exchange and archiving
scenarios this is advantageous; however, the fixed nature of the embedded information may become
a liability in large and sophisticated data management systems (see discussion chapter 3 Metadata
and Ch 7 Small Scale Approaches to Digital Storage Systems). This, and other limitations with BWF,
can be managed by using only a minimal set of data within BWF and maintaining other data with
external data management systems. AES31-2-2006, the AES standard on “Network and file transfer
of audio – Audio-file transfer and exchange – File format for transferring digital audio data between
systems of different type and manufacture” is largely compatible with the standard set in BWF, and
its is expected that future development in the area will continue to make the format viable. The
BWF format is widely accepted by the archiving community and with the limitations described in
mind IASA recommends the use of BWF .wav files [EBU Tech 3285] for archival purposes.
2.8.3
Multitrack audio and film or video soundtracks, or large audio files, may use RF64 [EBU Tech 3306],
which is compatible with BWF, AES-31 or as a wav file in an Media Exchange Format (MXF)
wrapper. As these are all still under development, one pragmatic approach may be to create multiple
time coherent mono BWF files wrapped in the tar (tape archive) format.
2.9
Audio Path: The combination of reproduction equipment, signal cables, mixers and other audio
processing equipment should have specifications that equal or exceed that of digital audio at the
specified sampling rate and bit depth. The replay equipment, audio path, target format and standards
must exceed that of the original carrier.
11
Chapter 3: Metadata
3.1
Introduction
3.1.1
Metadata is structured data that provides intelligence in support of more efficient operations on
resources, such as preservation, reformatting, analysis, discovery and use. It operates at its best in a
networked environment, but is still a necessity in any digital storage and preservation environment.
Metadata instructs end-users (people and computerised programmes) about how the data are
to be interpreted. Metadata is vital to the understanding, coherence and successful functioning of
each and every encounter with the archived object at any point in its lifecycle and with any objects
associated with or derived from it.
3.1.2
It will be helpful to think about metadata in functional terms as “schematized statements about
resources: schematized because machine understandable, [as well as human readable]; statements
because they involve a claim about the resource by a particular agent; resource because any
identifiable object may have metadata associated with it” (Dempsey 2005). Such schematized
(or encoded) statements (also referred to as metadata ‘instances’) may be very simple, a single
Uniform Resource Identifier (URI), within a single pair of angle brackets < > as a container or
wrapper and a namespace. Typically they may become highly evolved and modular, comprising many
containers within containers, wrappers within wrappers, each drawing on a range of namespace
schemas, and assembled at different stages of a workflow and over an extended period of time. It
would be most unusual for one person to create in one session a definitive, complete metadata
instance for any given digital object that stands for all time.
3.1.3
Regardless of how many versions of an audio file may be created over time, all significant properties
of the file that has archival status must remain unchanged. This same principle applies to any
metadata embedded in the object (see section 3.1.4 below). However, data about any object are
changeable over time: new information is discovered, opinions and terminology change, contributors
die and rights expire or are re-negotiated. It is therefore often advisable to keep audio files and all
or some metadata files separate, establish appropriate links between them, and update the metadata
as information and resources become available. Editing the metadata within a file is possible, though
cumbersome, and does not scale up as an appropriate approach for larger collections. Consequently,
the extent to which data is embedded in the files as well as in separate data management
system will be determined by the size of the collection, the sophistication of the particular data
management system, and the capabilities of the archive personnel.
3.1.4
Metadata may be integrated with the audio files and is in fact suggested as an acceptable solution
for a small scale approach to digital storage systems (see section 7.4 Basic Metadata). The Broadcast
Wave Format (BWF) standardized by the European Broadcasting Union (EBU), is an example of such
audio metadata integration, which allows the storage of a limited number of descriptive data within the
.wav file (see section 2.8 File Formats). One advantage of storing the metadata within the file is that it
removes the risk of losing the link between metadata and the digital audio. The BWF format supports
the acquisition of process metadata and many of the tools associated with that format can acquire
the data and populate the appropriate part of the BEXT (broadcast extension) chunk. . The metadata
might therefore include coding history, which is loosely defined in the BWF standard, and allows
the documentation of the processes that lead to the creation of the digital audio object. This shares
similarities with the event entity in PREMIS (see 3.5.2 , 3.7.3 and Fig.1 ). When digitizing from analogue
sources the BEXT chunk can also be used to store qualitative information about the audio content.
When creating a digital object from a digital source, such as DAT or CD, the BEXT chunk can be used
to record errors that might have occurred in the encoding process.
12
Metadata
A=<ANALOGUE> Information about the analogue sound signal path
A=<PCM> Information about the digital sound signal path
F=<48000, 441000, etc.> Sampling frequency [Hz]
W=<16, 18, 20, 22, 24, etc.> Word length [bits]
M=<mono, stereo, 2-channel> Mode
T=<free ASCII-text string> Text for comments
Coding History Field: BWF (http://www.ebu.ch/CMSimages/en/tec_text_r98-1999_tcm6-4709.pdf)
A=ANALOGUE, M=Stereo, T=Studer A820;SN1345;19.05;Reel;AMPEX 406
A=PCM, F=48000, W=24, M=Stereo, T=Apogee PSX-100;SN1516;RME DIGI96/8 Pro
A=PCM, F=48000, W=24, M=Stereo, T=WAV
A=PCM, F=48000, W=24, M=stereo, T=2006-02-20 File Parser brand name
A=PCM, F=48000, W=24, M=stereo, T=File Converter brand name 2006-02-20; 08:10:02
Fig. 1 National Library of Australia’s interpretation of the coding history of an original reel converted to BWF
using database and automated systems.
3.1.5
The Library of Congress has been working on formalising and expanding the various data chunks in
the BWF file. Embedded Metadata and Identifiers for Digital Audio Files and Objects: Recommendations
for WAVE and BWF Files Today is their latest draft available for comment at http://home.comcast.
net/~cfle/AVdocs/Embed_Audio_081031.doc. AES X098C is another development in the
documentation of process and digital provenance metadata.
3.1.6
There are however, many advantages to maintaining metadata and content separately, by employing, for
instance a framework standard such as METS (Metadata Encoding and Transmission Standard see section
3.8 Structural Metadata — METS). Updating, maintaining and correcting metadata is much simpler in a
separate metadata repository. Expanding the metadata fields so as to incorporate new requirements
or information is only possible in an extensible, and separate, system, and creating a variety of new ways
of sharing the information requires a separate repository to create metadata the can be used by those
systems. For larger collections the burden of maintaining metadata only in the headers of the BWF file
would be unsustainable. MPEG-7 requires that audio content and descriptive metadata are separated,
though descriptions can be multiplexed with the content as alternating data segments.
3.1.7
It is of course possible to wrap a BWF file with a much more informed metadata, and providing the
information kept in BWF is fixed and limited, this approach has the advantage of both approaches.
Another example of integration is the tag metadata that needs to be present in access files so
that a user may verify that the object downloaded or being streamed is the object that was
sought and selected. ID3, the tag used in MP3 files to describe content information which is readily
interpreted by most players, allows a minimum set of descriptive metadata. And METS itself has
been investigated as a possible container for packaging metadata and content together, though the
potential size of such documents suggests this may not be a viable option to pursue.
3.1.8
A general solution for separating the metadata from the contents (possibly with redundancy if the
contents includes some metadata) is emerging from work being undertaken in several universities
in liaison with major industrial suppliers such as SUN Microsystems, Hewlett-Packard and IBM. The
concept is to always store the representation of one resource as two bundled files: one including the
‘contents’ and the other including the metadata associated to that content. The second file includes:
3.1.8.1 The list of identifiers according to all the involved rationales. It is in fact a series of “aliases”
pertaining to the URN and the local representation of the resource (URL).
3.1.8.2 The technical metadata (bits per sample / sampling rate; accurate format definition; possibly
the associated ontology).
13
Metadata
3.1.9
3.1.8.3 The factual metadata (GPS coordinates / Universal time code / Serial number of the
equipment / Operator / …).
3.1.8.4 The semantic metadata.
In summary, most systems will adopt a practical approach that allows metadata to be both embedded
within files and maintained separately, establishing priorities (i.e. which is the primary source of
information) and protocols (rules for maintaining the data) to ensure the integrity of the resource.
3.2
Production
3.2.1
The rest of this chapter assumes that in most cases the audio files and the metadata files will be
created and managed separately. In which case, metadata production involves logistics — moving
information, materials and services through a network cost-effectively. However, a small scale
collection, or an archive in earlier stages of development, may find advantages in embedding
metadata in BWF and selectively populating a subset of the information described below. If done
carefully, and with due understanding of the standards and schemas discussed in this chapter, such
an approach is sustainable and will be migrate-able to a fully implemented system as described
below. Though a decision can be made by an archive to embed all or some metadata within the file
headers, or to manage only some data separately, the information within this chapter will still inform
this approach. (See also Chapter 7 Small Scale Approaches to Digital Storage Systems).
3.2.2
Until recently the producers of information about recordings either worked in a cataloguing
team or in a technical team and their outputs seldom converged. Networked spaces blur historic
demarcations. Needless to say, the embodiment of logistics in a successful workflow also requires
the involvement of people who understand the workings and connectivity of networked spaces.
Metadata production therefore involves close collaboration between audio technicians, Information
Technology (IT) and subject specialists. It also requires attentive management working to a clearly
stated strategy that can ensure workflows are sustainable and adaptable to the fast-evolving
technologies and applications associated with metadata production.
3.2.3
Metadata is like interest — it accrues over time. If thorough, consistent metadata has been created, it is
possible to predict this asset being used in an almost infinite number of new ways to meet the needs
of many types of user, for multi-versioning, and for data mining. But the resources and intellectual and
technical design issues involved in metadata development and management are not trivial. For example,
some key issues that must be addressed by managers of any metadata system include:
3.2.4
3.2.3.1 Identifying which metadata schema or extension schemas should be applied in order to
best meet the needs of the production teams, the repository itself and the users;
3.2.3.2 Deciding which aspects of metadata are essential for what they wish to achieve, and how
granular they need each type of metadata to be. As metadata is produced for the longterm there will likely always be a trade-off between the costs of developing and managing
metadata to meet current needs, and creating sufficient metadata that will serve future,
perhaps unanticipated demands;
3.2.3.3 Ensuring that the metadata schemas being applied are the most current versions.
3.2.3.4 Interoperability is another factor; in the digital age, no archive is an island. In order to send
content to another archive or agency successfully, there will need to be commonality of
structure and syntax. This is the principle behind METS and BWF.
A measure of complexity is to be expected in a networked environment where responsibility for the
successful management of data files is shared. Such complexity is only unmanageable, however, if we
cling to old ways of working that evolved in the early days of computers in libraries and archives —
14
Metadata
before the Web and XML. As Richard Feynman said of his own discipline, physics, ‘you cannot
expect old designs to work in new circumstances’. A new general set of system requirements and a
measure of cultural change are needed. These in turn will permit viable metadata infrastructures to
evolve for audiovisual archives.
3.3
Infrastructure
3.3.1
We do not need a ‘discographic’ metadata standard: a domain-specific solution will be an
unworkable constraint. We need a metadata infrastructure that has a number of core components
shared with other domains, each of which may allow local variations (e.g. in the form of extension
schema) that are applicable to the work of any particular audiovisual archive. Here are some of the
essential qualities that will help to define the structural and functional requirements:
3.3.1.1 Versatility: For the metadata itself, the system must be capable of ingesting, merging, indexing,
enhancing, and presenting to the user, metadata from a variety of sources describing a variety
of objects, It must also be able to define logical and physical structures, where the logical
structure represents intellectual entities, such as collections and works, while the physical
structure represents the physical media (or carriers) which constitute the source for the
digitized objects . The system must not be tied to one particular metadata schema: it must
be possible to mix schema in application profiles (see 3.9.8) suited to the archive’s particular
needs though without compromising interoperability. The challenge is to build a system that
can accommodate such diversity without needless complication for low threshold users, nor
prevent more complex activities for those requiring more room for manoeuvre.
3.3.1.2 Extensibility: Able to accommodate a broad range of subjects, document types
(e.g. image and text files) and business entities (e.g. user authentication, usage licenses,
acquisition policies, etc.). Allow for extensions to be developed and applied or ignored
altogether without breaking the whole, in other words be hospitable to experimentation:
implementing metadata solutions remains an immature science.
3.3.1.3 Sustainability: Capable of migration, cost-effective to maintain, usable, relevant and fit for
purpose over time.
3.3.1.4 Modularity: The systems used to create or ingest metadata, and merge, index and export it
should be modular in nature so that it is possible to replace a component that performs a
specific function with a different component, without breaking the whole.
3.3.1.5 Granularity: Metadata must be of a sufficient granularity to support all intended uses.
Metadata can easily be insufficiently granular, while it would be the rare case where
metadata would be too granular to support a given purpose.
3.3.1.6 Liquidity: Write once, use many times. Liquidity will make digital objects and representations
of those objects self-documenting across time, the metadata will work harder for the
archive in many networked spaces and provide high returns for the original investments of
time and money.
3.3.1.7 Openness and transparency: Supports interoperability with other systems. To facilitate
requirements such as extensibility, the standards, protocols, and software incorporated
should be as open and transparent as possible.
3.3.1.8 Relational (hierarchy/sequence/provenance): Must express parent-child relationships, correct
sequencing, e.g. the scenes of a dramatic performance, and derivation. For digitized items, be
able to support accurate mappings and instantiations of original carriers and their intellectual
content to files. This helps ensure the authenticity of the archived object (Tennant 2004).
15
Metadata
3.3.2
This recipe for diversity is itself a form of openness. If an open W3C (World Wide Web
Consortium) standard, such as Extensible Markup Language (XML), a widely adopted mark-up
language, is selected then this will not prevent particular implementations from including a mixture
of standards such as Material Exchange Format (MXF) and Microsoft’s Advanced Authoring Format
(AAF) interchange formats.
3.3.3
Although MXF is an open standard, in practice the inclusion of metadata in the MXF is commonly
made in a proprietary way. MXF has further advantages for the broadcast industry because it can
be used to professionally stream content whereas other wrappers only support downloading the
complete file. The use of MXF for wrapping contents and metadata would only be acceptable
for archiving after the replacement of any metadata represented in proprietary formats by open
metadata formats.
3.3.4
So much has been written and said about XML that it would be easy to regard it as a panacea. XML
is not a solution in itself but a way of approaching content organisation and re-use, its immense
power harnessed through combining it with an impressive array of associated tools and technologies
that continue to be developed in the interests of economical re-use and repurposing of data. As
such, XML has become the de-facto standard for representing metadata descriptions of resources on
the Internet. A decade of euphoria about XML is now matched by the means to handle it thanks to
the development of many open source and commercial XML editing tools (See 3.6.2).
3.3.5
Although reference is made in this chapter to specific metadata formats that are in use today, or that
promise to be useful in the future, these are not meant to be prescriptive. By observing those key
qualities in section 3.3.1 and maintaining explicit, comprehensive and discrete records of all technical
details, data creation and policy changes, including dates and responsibility, future migrations and
translations will not require substantial changes to the underlying infrastructure. A robust metadata
infrastructure should be able to accommodate new metadata formats by creating or applying tools
specific to that format, such as crosswalks, or algorithms for translating metadata from one encoding
scheme to another in an effective and accurate manner. A number of crosswalks already exist for
formats such as MARC, MODS, MPEG-7 Path, SMPTE and Dublin Core. Besides using crosswalks
to move metadata from one format to another, they can also be used to merge two or more
different metadata formats into a third, or into a set of searchable indexes. Given an appropriate
container/transfer format, such as METS, virtually any metadata format such as MARC-XML, Dublin
Core, MODS, SMPTE (etc), can be accommodated. Moreover, this open infrastructure will enable
archives to absorb catalogue records from their legacy systems in part or in whole while offering
new services based on them, such as making the metadata available for harvesting — see OAI-PMH
(Open Archives Initiative Protocol for Metadata Harvesting).
3.4
Design — Ontologies1
3.4.1
Having satisfied those top-level requirements, a viable metadata design, in all its detail, will take its shape
from an information model or ontology. Several ontologies may be relevant depending on the number
of operations to be undertaken. CIDOC’s CRM (Conceptual Reference Model http://cidoc.ics.forth.gr/)
is recommended for the cultural heritage sector (museums, libraries and archives); FRBR (Functional
1
W3C definition: An ontology defines the terms used to describe and represent an area of knowledge. Ontologies are used
by people, databases, and applications that need to share domain information (a domain is just a specific subject area or area
of knowledge, like medicine, tool manufacturing, real estate, automobile repair, financial management, etc.). Ontologies include
computer-usable definitions of basic concepts in the domain and the relationships among them (note that here and throughout
this document, definition is not used in the technical sense understood by logicians). They encode knowledge in a domain and also
knowledge that spans domains. In this way, they make that knowledge reusable.
16
Metadata
Requirements for Bibliographic Records http://www.loc.gov/cds/FRBR.html) will be appropriate for an
archive consisting mainly of recorded performances of musical or literary works, its influence enhanced
by close association with RDA (Resource Description and Access) and DCMI (Dublin Core Metadata
Initiative). COA (Contextual Ontology Architecture http://www.rightscom.com/Portals/0/Formal_
Ontology_for_Media_Rights_Transactions.pdf) will be fit for purpose if rights management is paramount,
as will the Motion Picture Experts Group rights management standard, MPEG-21. RDF (Resource
Description Framework http://www.w3.org/RDF/), a versatile and relatively light-weight specification,
should be a component especially where Web resources are being created from the archival repository:
this in turn admits popular applications such as RSS (Really Simple Syndication) for information feeds
(syndication). Other suitable candidates that improve the machine handling and interpretation of the
metadata may be found in the emerging ‘family’ of ontologies created using OWL (Web Ontology
Language).The definition of ontologies and the reading of ontologies expressed in OWL can easily be
made using “Protégé”, an open tool of the Stanford University: http://protege.stanford.edu/. OWL can be
used from a simple definition of terms up to a complex object oriented modelling.
3.5
Design — Element sets
3.5.1
A metadata element set comes next in the overall design. Here three main categories or groupings
of metadata are commonly described:
3.5.2
3.5.3
3.5.1.1 Descriptive Metadata, which is used in the discovery and identification of an object.
3.5.1.2 Structural Metadata, which is used to display and navigate a particular object for a user and
includes the information on the internal organization of that object, such as the intended
sequence of events and relationships with other objects, such as images or interview
transcripts.
3.5.1.3 Administrative Metadata, which represents the management information for the object
(such as the namespaces that authorise the metadata itself), dates on which the object
was created or modified, technical metadata (its validated content file format, duration,
sampling rate, etc.), rights and licensing information. This category includes data essential
to preservation.
All three categories, descriptive, structural and administrative, must be present regardless of the
operation to be supported, though different sub-sets of the data may exist in any file or instantiation.
So, if the metadata supports preservation — “information that supports and documents the digital
preservation process” (PREMIS) — then it will be rich in data about the provenance of the object,
its authenticity and the actions performed on it. If it supports discovery then some or all of the
preservation metadata will be useful to the end user (i.e. as a guarantor of authenticity) though it
will be more important to elaborate and emphasise the descriptive, structural and licensing data
and provide the means for transforming the raw metadata into intuitive displays or in readiness
for harvesting or interaction by networked external users. Needless to say, an item that cannot be
found can neither be preserved nor listened to so the more inclusive the metadata, with regard to
these operations, the better.
Each of those three groupings of metadata may be compiled separately: administrative (technical)
metadata as a by-product of mass-digitization; descriptive metadata derived from a legacy database
export; rights metadata as clearances are completed and licenses signed. However, the results
of these various compilations need to be brought together and maintained in a single metadata
instance or set of linked files together with the appropriate statements relating to preservation.
It will be essential to relate all these pieces of metadata to a schema or DTD (Document Type
Definition) otherwise the metadata will remain just a ‘blob’, an accumulation of data that is legible for
humans but unintelligible for machines.
17
Metadata
3.6
Design — Encoding and Schemas
3.6.1
In the same way that audio signals are encoded to a WAV file, which has a
published specification, the element set will need to be encoded: XML, perhaps combined with
RDF, is the recommendation stated above. This specification will be declared in the first line of
any metadata instance <?xml version=”1.0” encoding=”UTF-8” ?> . This by itself provides little
intelligence: it is like telling the listener that the page of the CD booklet they are reading is made
of paper and is to be held in a certain way. What comes next will provide intelligence (remember,
to machines as well as people) about the predictable patterns and semantics of data to be
encountered in the rest of the file. The rest of the metadata file header consists typically of a
sequence of namespaces for other standards and schema (usually referred to as ‘extension schema’)
invoked by the design.
<mets:mets xmlns:mets=”http://www.loc.gov/standards/mets/”
xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance”
xmlns:dc=”http://dublincore.org/documents/dces/”
xmlns:xlink=”http://www.w3.org/TR/xlink”
xmlns:dcterms=”http://dublincore.org/documents/dcmi-terms/”
xmlns:dcmitype=”http://purl.org/dc/dcmitype”
xmlns:tel=”http://www.theeuropeanlibrary.org/metadatahandbook/telterms.html”
xmlns:mods=”http://www.loc.gov/mods”
xmlns:cld=”http://www.ukoln.ac.uk/metadata/rslp/schema/”
xmlns:blap=”http://labs.bl.uk/metadata/blap/terms.html”
xmlns:marcrel=”http://www.loc.gov/loc.terms/relators/”
xmlns:rdf=”http://www.w3.org/1999/02/22-rdf-syntax-ns#type”
xmlns:blapsi=”http://sounds.bl.uk/blapsi.xml” xmlns:namespace-prefix=”blapsi”>
Fig 2: Set of namespaces employed in the British Library METS profile for sound recordings
3.6.2
Such intelligent specifications, in XML, are called XML schema, the successor to DTD. DTDs are still
commonly encountered on account of the relative ease of their compilation. The schema will reside
in a file with the extension .xsd (XML Schema Definition) and will have its own namespace to which
other operations and implementations can refer. Schemas require expertise to compile. Fortunately
open source tools are available that enable a computer to infer a schema from a well-formed
XML file . Tools are also available to convert xml into other formats, such as .pdf or .rtf (Word)
documents into XML. The schema may also incorporate the idealised means for displaying the data
as an XSLT file. Schema (and namespaces) for descriptive metadata will be covered in more detail in
3.9 Descriptive Metadata — Application Profiles, Dublin Core (DC) below.
3.6.3
To summarise the above relationships, an XML Schema or DTD describes an XML structure that
marks up textual content in the format of an XML encoded file. The file (or instance) will contain
one or more namespaces representing the extensionr schema that further qualify the XML
structure to be deployed.
3.7
Administrative Metadata — Preservation Metadata
3.7.1
The information described in this section is part of the administrative metadata grouping. It
resembles the header information in the audio file and encodes the necessary operating information.
In this way the computer system recognises the file and how it is to be used by first associating
the file extension with a particular type of software, and reading the coded information in the file
header. This information must also be referenced in a separate file to facilitate management and
18
Metadata
aid in future access because file extensions are at best ambiguous indicators of the functionality
of the file. The fields which describe this explicit information, including type and version, can be
automatically acquired from the headers of the file and used to populate the fields of the metadata
management system. If an operating system, now or in the future, does not include the ability to play
a .wav file or read an .xml instance for example, then the software will be unable to recognise the
file extension and will not be able to access the file or determine its type. By making this information
explicit in a metadata record, we make it possible for future users to use the preservation
management data and decode the information data. The standards being developed in AES-X098B
which will be released by the Audio Engineering Society as AES57 “AES standard for audio metadata
— audio object structures for preservation and restoration” codify this aspiration.
3.7.2
Format registries now exist, though are still under development, that will help to categorise and
validate file formats as a pre-ingest task: PRONOM (online technical registry, including file formats,
maintained by TNA (The National Archives, UK), which can be used in conjunction with another
TNA tool DROID (Digital Record Object Identification — that performs automated batch
identification of file formats and outputs metadata). From the U.S, Harvard University GDFR
(Global Digital Format Registry) and JHOVE (JSTOR/Harvard Object Validation Environment
identification, validation, and characterization of digital objects) offer comparable services in support
of preservation metadata compilation. Accurate information about the file format is the key to
successful long-term preservation.
3.7.3
Most important is that all aspects of preservation and transfer relating to audio files, including all
technical parameters are carefully assessed and kept. This includes all subsequent measures carried
out to safeguard the audio document in the course of its lifetime. Though much of the metadata
discussed here can be safely populated at a later date the record of the creation of the digital
audio file, and any changes to its content, must be created at the time the event occurs. This history
metadata tracks the integrity of the audio item and, if using the BWF format, can be recorded as
part of the file as coding history in the BEXT chunk. This information is a vital part of the PREMIS
preservation metadata recommendations. Experience shows that computers are capable of
producing copious amounts of technical data from the digitization process. This may need to be
distilled in the metadata that is to be kept. Useful element sets are proposed in the interim set
AudioMD (http://www.loc.gov/rr/mopic/avprot/audioMD_v8.xsd), an extension schema developed
by Library of Congress, or the AES audioObject XML schema which at the time of writing is under
review as a standard.
3.7.4
If digitising from legacy collections, these schemas are useful not only for describing the digital file,
but also the physical original. Care needs to be taken to avoid ambiguity about which object is being
described in the metadata: it will be necessary to describe the work, its original manifestation and
subsequent digital versions but it is critical to be able to distinguish what is being described in each
instance. PREMIS distinguishes the various components in the sequence of change by associating
them with events, and linking the resultant metadata through time.
3.8
Structural Metadata — METS
3.8.1
Time-based media are very often multimedia and complex. A field recording may consist of a
sequence of events (songs, dances, rituals) accompanied by images and field notes. A lengthy oral
history interview occupying more than one .wav file may also be accompanied by photographs of
the speakers and written transcripts or linguistic analysis. Structural metadata provides an inventory
of all relevant files and intelligence about external and internal relationships including preferred
19
Metadata
sequencing, e.g. the acts and scenes of an operatic recording. METS (Metadata Encoding and
Transmission Standard, current version is 1.7) with its structural map (structMap) and file group
(fileGrp) sections has a recent but proven track record of successful applications in audiovisual
contexts (see fig. 3).
METS instance for a recording
on two sides of one disc
Header
Descriptive
Metadata
parent:Disc
parent:Set
child:Side
wav 1
child:Side
wav 2
child:Label
tiff 1
child:Label
tiff 2
Administrative MD:
Technical MD
Rights MD
Provenance MD
Key
metsHdr
dmdSec
structMap
fileSec
amdSec
Fig 3: components of a METS instance and one possible set of relationships among them
3.8.2
The components of a METS instance are:
3.8.2.1 A header describes the METS object itself, such as who created this object, when, for what
purpose. The header information supports management of the METS file proper.
3.8.2.2 The descriptive metadata section contains information describing the information resource
represented by the digital object and enables it to be discovered.
3.8.2.3 The structural map, represented by the individual leaves and details, orders the digital files
of the object into a browsable hierarchy.
3.8.2.4 The content file section, represented by images one through five, declares which digital
files constitute the object. Files may be either embedded in the object or referenced.
3.8.2.5 The administrative metadata section contains information about the digital files declared in
the content file section. This section subdivides into:
3.8.2.5.1technical metadata, specifying the technical characteristics of a file
3.8.2.5.2source metadata, specifying the source of capture (e.g.,direct capture or reformatted 4 x 5
transparency)
3.8.2.5.3digital provenance metadata, specifying the changes a file has undergone since its birth
3.8.2.5.4rights metadata, specifying the conditions of legal access.
3.8.2.6 The sections on technical metadata, source metadiata, and digital provenance metadata
carry the information pertinent to digital preservation.
20
Metadata
3.8.2.7 For the sake of completeness, the behaviour section, not shown above in Fig. 2, associates
executables with a METS object. For example, a METS object may rely on a certain piece of code to
instantiate for viewing, and the behavior section could reference that code.
3.8.3
3.8.4
Structural metadata may need to represent additional business objects:
3.8.3.1 user information (authentication)
3.8.3.2 rights and licenses (how an object may be used)
3.8.3.3 policies (how an object was selected by the archive)
3.8.3.4 services (copying and rights clearance)
3.8.3.5 organizations (collaborations, stakeholders, sources of funding).
These may be represented by files referenced to a specific address or URL. Explanatory annotations
may be provided in the metadata for human readers.
3.9
Descriptive Metadata — Application Profiles, Dublin Core (DC)
3.9.1
Much of the effort devoted to metadata in the heritage sector has focussed on descriptive metadata
as an offshoot of traditional cataloguing. However, it is clear that too much attention in this area
(e.g. localised refinements of descriptive tags and controlled vocabularies) at the expense of other
considerations described above will result in system shortcomings overall. Figure 4 demonstrates the
various inter-dependencies that need to be in place, descriptive metadata tags being just one sub-set
of all the elements in play.
Simple descriptive metadata
Cataloging rules
Controlled vocabs…
Application profile
‘Element set’
MARC21
DC
VRA Core
MODS
Onix
…
RDF
Values/content
XML
ISO2709
…
FRBR
INDECS
CIDOC
…
Information
model
Encoding
Fig 4: simple descriptive metadata (courtesy Dempsey, CLIR/DLF primer, 2005)
3.9.2
Interoperability must be a key component of any metadata strategy: elaborate systems devised
independently for one archival repository by a dedicated team will be a recipe for low productivity,
high costs and minimal impact. The result will be a metadata cottage industry incapable of expansion.
Descriptive metadata is indeed a classic case of Richard Gabriel’s maxim ‘Worse is better’. Comparing
two programme languages, one elegant but complex, the other awkward but simple, Gabriel predicted,
correctly, that the language that was simpler would spread faster, and as a result, more people
would come to care about improving the simple language than improving the complex one. This is
21
Metadata
demonstrated by the widespread adoption and success of Dublin Core (DC), initially regarded as an
unlikely solution by the professionals on account of its rigorous simplicity.
3.9.3
The mission of DCMI (DC Metadata Initiative) has been to make it easier to find resources
using the Internet through developing metadata standards for discovery across domains, defining
frameworks for the interoperation of metadata sets and facilitating the development of communityor discipline-specific metadata sets that are consistent with these aims. It is a vocabulary of just
fifteen elements for use in resource description and provides economically for all three categories
of metadata. None of the elements is mandatory: all are repeatable, although implementers may
specify otherwise in application profiles — see section 3.9.8 below. The name “Dublin” is due to its
origin at a 1995 invitational workshop in Dublin, Ohio; “core” because its elements are broad and
generic, usable for describing a wide range of resources. DC has been in widespread use for more
than a decade and the fifteen element descriptions have been formally endorsed in the following
standards: ISO Standard 15836-2003 of February 2003 [ISO15836 http://dublincore.org/documents/
dces/#ISO15836 ] NISO Standard Z39.85-2007 of May 2007 [NISOZ3985 http://dublincore.org/
documents/dces/#NISOZ3985 ] and IETF RFC 5013 of August 2007 [RFC5013 http://dublincore.
org/documents/dces/#RFC5013].
Table 1 (below) lists the fifteen DC elements with their (shortened) official definitions and suggested
interpretations for audiovisual contexts.
DC element
Title
Subject
Description
Creator
Publisher
Contributor
Date
Type
Format
DC definition
A name given to the resource
Audiovisual interpretation
The main title associated with the
recording.
The topic of the resource.
Main topics covered
An account of the resource.
Explanatory notes, interview
summaries, descriptions of
environmental or cultural context,
list of contents.
An entity primarily responsible for making
Not authors or composers of the
the resource.
recorded works but the name of
the archive.
An entity responsible for making the
Not the publisher of the original
resource available.
document that has been digitized.
Typically the publisher will be the
same as the Creator.
An entity responsible for making
Any named person or sound
contributions to the resource.
source. Will need suitable qualifier,
such as role (e.g. performer,
recordist)
A point or period of time associated with an Not the recording or (P) date of
event in the lifecycle of the resource.
the original but a date relating to
the resource itself.
The nature or genre of the resource.
The domain of the resource, not
the genre of the music. So Sound,
not Jazz.
The file format, physical medium, or
The file format, not the original
dimensions of the resource.
physical carrier.
22
Metadata
DC element
Identifier
Source
Language
Relation
Coverage
Rights
DC definition
An unambiguous reference to the resource
within a given context.
A related resource from which the
described resource is derived.
Likely to be the URI of the audio
file.
A reference to a resource from
which the present resource is
derived
A language of the resource.
A language of the resource
A related resource.
Reference to related objects.
The spatial or temporal topic of the
What the recording exemplifies,
resource, the spatial applicability of the
e.g. a cultural feature such as
resource, or the jurisdiction under which the traditional songs or a dialect.
resource is relevant.
Information about rights held in and over
Information about rights held in
the resource.
and over the resource
Table 1: The DC 15 elements
3.9.4
The elements of DC have been expanded to include further properties. These are referred to as DC
Terms. A number of these additional elements (‘terms’) will be useful for describing time-based media:
DC Term
Alternative
DC definition
Any form of the title used as a substitute
or alternative to the formal title of the
resource.
Extent
extentOriginal
The size or duration of the resource.
The physical or digital manifestation of the
resource.
Spatial characteristics of the intellectual
content of the resource.
Spatial
Temporal
Created
Temporal characteristics of the intellectual
content of the resource.
Date of creation of the resource
An alternative title, e.g. a translated
title, a pseudonym, an alternative
ordering of elements in a generic
title.
File size and duration
The size or duration of the original
source recording(s)
Recording location, including
topographical co-ordinates to
support map interfaces
Occasion on which recording was
made.
Recording date and any other
significant date in the lifecycle of
the recording.
Table 2: DC Terms (a selection)
3.9.5
Implementers of DC may choose to use the fifteen elements either in their legacy dc: variant
(e.g., http://purl.org/dc/elements/1.1/creator) or in the dcterms: variant (e.g., http://purl.org/dc/
terms/creator) depending on application requirements. Over time, however, and especially if RDF
is part of the metadata strategy, implementers are expected (and encouraged by DCMI) to use
the semantically more precise dcterms: properties, as they more fully comply with best practice for
machine-processable metadata.
3.9.6
Even in this expanded form, DC may lack the fine granularity required in a specialised audiovisual
archive. The Contributor element, for example, will typically need to mention the role of the
Contributor in the recording to avoid, for instance, confusing performers with composers or actors
with dramatists. A list of common roles (or ‘relators’) for human agents has been devised (MARC
relators) by the Library of Congress. Here are two examples of how they can be implemented.
23
Metadata
<dcterms:contributor>
<marcrel:CMP>Beethoven, Ludwig van, 1770-1827</marcrel:CMP>
<marcrel:PRF>Quatuor Pascal</marcrel:PRF>
</dcterms:contributor>
<dcterms:contributor>
<marcrel:SPK>Greer, Germaine, 1939- (female)</marcrel:SPK>
<marcrel:SPK>McCulloch, Joseph, 1908-1990 (male)</marcrel:SPK>
</dcterms:contributor>
The first example tags ‘Beethoven’ as the composer (CMP) and ‘Quatuor Pascal’ as the performer
(PRF). The second tags both contributors, Greer and McCulloch, as speakers (SPK) though does not
go as far as determining who is the interviewer and who is the interviewee. That information would
need to be conveyed elsewhere in the metadata, e.g. in Description or Title.
3.9.7
In this respect, other schema may be preferable, or could be included as additional extension
schema (as illustrated in Fig. 2). MODS (Metadata Object Description Schema http://www.loc.gov/
standards/mods/), for instance allows for more granularity in names and linkage with authority files, a
reflection of its derivation from the MARC standard:
name
Subelements:
namePart
Attribute: type (date, family, given, termsOfAddress)
displayForm
affiliation
role
roleTerm
Attributes: type (code, text); authority
(see: www.loc.gov/marc/sourcecode/relator/relatorsource.html)
description
Attributes: ID; xlink; lang; xml:lang; script; transliteration
type (enumerated: personal, corporate, conference)
authority (see: www.loc.gov/marc/sourcecode/authorityfile/authorityfilesource.html)
3.9.8
Using METS it would be admissible to include more than one set of descriptive metadata suited
to different purposes, for example a Dublin Core set (for OAI-PMH (Open Archives Initiative
Protocol for Metadata Harvesting) compliance) and a more sophisticated MODS set for compliance
with other initiatives, particularly exchange of records with MARC encoded systems. This ability to
incorporate other standard approaches is one of the advantages of METS.
3.9.9
DC, under the governance of the Dublin Core Metadata Initiative (DCMI), continues to develop.
On the one hand its value for networking resources is strengthened through closer association
with semantic web tools such as RDF (see Nilsson et al, DCMI 2008) while on the other it aims
to increase its relevance to the heritage sector through a formal association with RDA (Resource
Description &Access http://www.collectionscanada.gc.ca/jsc/rda.html) due to be released in 2009.
As RDA is seen as a timely successor to the Anglo America Cataloguing Rules this particular
development may have major strategic implications for audiovisual archives that are part of
national and university libraries. For broadcasting archives other developments based on DCMI
are noteworthy At the time of writing the EBU (European Broadcast Union) is completing the
development of the EBU Core Metadata Set, which is based on and compatible with Dublin Core. Guidelines on the Production and Preservation of Digital Audio Objects
24
Metadata
3.9.10 The archive may wish to modify (expand, adapt) the core element set. Such modified sets, drawing
on one or more existing namespace schemas (e.g. MODS and/or IEEE LOM as well as DC) are
known as application profiles. All elements in an application profile are drawn from elsewhere, from
distinct namespace schemas. If implementers wish to create ‘new’ elements that are not schematized
elsewhere, for instance contributor roles unavailable in the MARC relators set (e.g. non-human
agents such as species, machines, environments), then they must create their own namespace
schema, and take responsibility for ‘declaring’ and maintaining that schema.
3.9.11 Application profiles include a list of the governing namespaces together with their current URL
(preferably PURL — permanent URL). These are replicated in each metadata instance. There then
follows a list of each data element together with permitted values and style of content. This may
refer to in-house or additional rules and controlled vocabularies, e.g. thesauri of instrument names
and genres, authority files of personal names and subjects. The profile will also specify mandatory
schemes for particular elements such as dates (YYYY-MM-DD) and geographical co-ordinates and
such standardised representations of location and time will be able to support map and timeline
displays as non-textual retrieval devices.
Name of Term
Term URI
Label
Defined By
Source Definition
BLAP-S Definition
Source Comments
BLAP-S Comments
Type of term
Refines
Refined by
Has encoding scheme
Obligation
Occurrence
Title
http://purl.org/dc/elements/1.1/title
Title
http://dublincore.org/documents/dcmi-terms/
A name given to a resource
The title of the work or work component
Typically, a Title will be a name by which the source is formally known.
If no title is available construct one that is derived from the resource or
supply [no title]. Follow normal cataloguing practice for recording title in other
languages using the ‘Alternative’ refinement. Where data are derived from the
Sound Archive catalogue, this will equate to one of the following title fields in
the following hierarchical order: Work title (1), Item title (2), Collection title (3),
Product title (4), Original species (5) Broadcast title (6), Short title (7), Published
series (8), Unpublished series (9).
Element
Alternative
Mandatory
Not repeatable
Fig 5: Part of the British Library’s application profile of DC for sound (BLAP-S):
Namespaces used in this Application Profile
DCMI Metadata Terms http://dublincore.org/documents/dcmi-terms/
RDF http://www.w3.org/RDF/
MODS elements http://www.loc.gov/mods
TEL terms http://www.theeuropeanlibrary.org/metadatahandbook/telterms.html
BL Terms http://labs.bl.uk/metadata/blap/terms.html
MARCREL http://www.loc.gov/loc.terms/relators/
25
Metadata
3.9.12 The application profile therefore incorporates or draws on a data dictionary (a file defining the basic
organisation of a database down to its individual fields and field types) or several data dictionaries,
that may be maintained by an individual archive or shared with a community of archives. The
PREMIS data dictionary (http://www.loc.gov/standards/premis/v2/premis-2-0.pdf currently version 2)
relating exclusively to preservation is expected to be drawn on substantially. Its numerous elements
are known as ‘Semantic units’. Preservation metadata provides intelligence about provenance,
preservation activity, technical features, and aids in verifying the authenticity of a digital object. The
PREMIS Working Group released its Data Dictionary for Preservation metadata in June 2005 and
recommends its use in all preservation repositories regardless of the type of materials archived and
the preservation strategies employed.
3.9.13 By defining application profiles and, most importantly by declaring them, implementers can share
information about their schemas in order to collaborate widely on universal tasks such as long-term
preservation.
3.10 Sources of Metadata
3.10.1 Archives should not expect to create all descriptive metadata by themselves from scratch (the old
way). Indeed, given the in-built lifecycle relationship between resources and metadata such a notion
will be unworkable. There are several sources of metadata, especially the descriptive category that
should be exploited to reduce costs and provide enrichment through extending the means of input.
There are three main sources: professional, contributed and intentional (Dempsey:2007): they may
be deployed alongside each other.
3.10.2 Professional sources means drawing on the locked-in value of legacy databases, authority files and
controlled vocabularies which are valuable for published or replicated materials. It includes industry
databases, as well as archive catalogues. Such sources, especially archive catalogues, are notoriously
incomplete and incapable of interoperation without sophisticated conversion programmes and
complex protocols. There are almost as many data standards in operation in the recording and
broadcasting industries and the audiovisual heritage sector as there are separate databases. The lack
of a universal resolver for AV, such as ISBN for print, is a continuing hindrance and after decades of
discographical endeavour there is still disagreement about what constitutes a catalogue record: is
it an individual track or is it a sequence of tracks that make up an intellectual unit such as a multisectioned musical or literary work? Is it the sum total of tracks on a single carrier or set of carriers,
in other words, is the physical carrier the catalogue unit? Evidently, an agency that has chosen one
of the more granular definitions will find it much easier to export its legacy data successfully into a
metadata infrastructure. Belt and braces approaches to data export based on Z39.50
(http://www.loc.gov/z3950/agency/ protocol for information retrieval) and SRW/SRU (a protocol
for search and retrieve via standardized URL’s with a standardized XML response) will continue
to provide a degree of success, as will the ability of computers to harvest metadata from a central
resource. However, more effective investment should be made in the shared production of
resources which identify and describe names, subjects, places, time periods, and works.
3.10.3 Contributed sources means user generated content. A major phenomenon of recent years has
been the emergence of many sites which invite, aggregate and mine data contributed by users, and
mobilize that data to rank, recommend and relate resources. These include, for example, YouTube
and LastFM. These sites have value in that they reveal relations between people and between people
and resources as well as information about the resources themselves. Libraries have begun to
experiment with these approaches and there are real advantages to be gained by allowing users to
26
Metadata
augment professionally sourced metadata. So-called Web 2.0 features that support user contribution
and syndication are becoming commonplace features of available content management systems.
3.10.4 Intentional means data collected about use and usage that can enhance resource discovery. The
concept is borrowed from the commercial sector, Amazon recommendations, for instance, that are
based on aggregate purchase choices. Similar algorithms could be used to rank objects in a resource.
This type of data has emerged as a central factor in successful websites, providing useful paths
through intimidating amounts of complex information.
3.11 Future Development Needs
3.11.1 For all the recent work and developments, metadata remains an immature science, though this
chapter will have demonstrated that a number of substantial building blocks (data dictionaries,
schemas, ontologies, and encodings) are now in place to begin to match the appetite of researchers
for more easily accessible AV content and the long-held ambition of our profession to safeguard its
persistence. To achieve faster progress it will be necessary to find common ground between public
and commercial sectors and between the different categories of audiovisual archives, each of which
has been busy devising its own tools and standards.
3.11.2 Some success has been achieved with automatic derivation of metadata from resources. We need
to do more, especially as existing manual processes do not scale very well. Moreover, metadata
production does not look sustainable unless more cost is taken out of the process. “We should
not be adding cost and complexity, which is what tends to happen when development is through
multiple consensus-making channels which respond to the imperatives of a part only of the service
environment” (Dempsey:2005).
3.11.3 The problem of the reconciliation of databases, i.e. the capacity of the system to understand that
items are semantically identical although they may be represented in different ways, remains an open
issue. There is significant research being undertaken to resolve this issue, but a widely suitable general
solution has yet to emerge. This issue is also very important for the management of the persistence in
the OAIS as the following example demonstrates. The semantic expression that Wolfgang Amadeus
Mozart is the composer of most of the parts of the Requiem (K. 626) is represented in a totally
different way in FRBR modelling when compared to a list of simple DCMI statements. In CDMI
‘Composer’ is a refinement of ‘contributor’ and ‘Mozart’ is its property; while in FRBR modelling,
‘composer’ is a relation between a physical person and an opus. The use of controlled vocabularies is
also a way of ensuring that W.A. Mozart represents the same person as Mozart.
27
Chapter 4: Unique and Persistent Identifiers
4.1
Introduction
4.1.1
A digital sound recording, whether stored on a mass storage system or on discrete carriers, must
be able to be identified and retrieved. An item cannot be considered preserved if it cannot be
located, nor linked to the catalogue and metadata record that gives it meaning. There is a need for
every digital item to be unambiguously and uniquely named. In ensuring that the digital object is
unambiguously and uniquely named the first step in the identification is to determine what is being
named, and at what level.
4.1.2
All computer records by their very nature have some sort of system identifier that enables them
to be stored without conflict. This identifier may be an acceptable public identifier, but more
often than not such identifiers are system oriented and subject to change based on system
requirements. There is a subsequent need for a persistent public identifier to maintain an item’s
accessibility, to ensure that it can be located and displayed by those who wish to use it so that
citations and links made to it continue to provide access to it. There is also a requirement for that
identifier to resolve to the item to which it refers regardless of where it has been stored or what
its system identifier may have become.
4.1.3
The Resource Description Framework (RDF) standard is an important reference for the identification
of digital objects (http://www.w3.org/RDF/ ). RDF is based on the concept of identifying things using
Web identifiers called URIs (Universal Resource Identifiers). The identification systems are based on
two basic mechanisms. The first is the naming of an item by creating an identifier based on semantics
or other rules of labelling such that the identifier will remain attached to the item. In the RDF standard,
such identifiers are called URNs (Universal Resource Names). The second is the locator, which is
organising a location system so that the item intended to be identified could be found from the
locator. In the RDF standard, such identifiers are called URLs (Universal Resource Locator).
4.1.4
There have been many proposed schemes for naming a digital object, some specifically for audio
or audiovisual objects, amongst them the EBU Technical Recommendation R99-1999 ‘Unique’
Source Identifier (USID) for use in the <OriginatorReference> field of the Broadcast Wave Format
(BWF). Such schemes are intended to provide a unique number within a particular community. Such
schemes have not been successful in obtaining universal acceptance.
4.2
Persistent Identifiers
4.2.1
Even before the issue of digitisation made it critical, libraries, archives and audio collections generally
have tended to develop systems with varying degrees of sophistication, which allow them to access
their materials. These numbering systems, which tend to be unique within their own domain, can
be incorporated into more universal naming schemes with the addition of a unique name for the
domain or institution. This kind of structure allows maximum flexibility to an organisation in the local
identification of its resources, whilst allowing the identifiers to be incorporated into a global system
with the addition of an appropriate naming authority component. These persistent identifiers are for
the user of the content to be able to identify a work (as opposed to a file) which remains constant
through time as a reference for that work regardless of how the file naming conventions have changed.
4.2.2
A Persistent Identifier (PID) is an identifier constructed and implemented such that the identified
resource will remain the same independently of the location of its representation and independent
of the fact that several copies are available at various locations. It means that the PIDs are URNs.
28
Unique and Persistent Identifiers
4.3
File Naming Conventions and Unique Identifiers
4.3.1
Care should be taken when discussing this subject to maintain the distinction between the persistent
identifier used to refer to a work, and the file naming conventions. In many practical system there
may well be links between the two. This section makes recommendations about file naming
conventions. Data files managed in any given repository may include several types of data, not just
audio. A Unique Identifier (UID) uniquely identifies a resource. This means that the identifier may
change for the particular embodiment of the resource and each copy of the resource has its own
ID. It consequently means that the UID are URL’s. For the purposes of this discussion, file names will
also be referred to as unique identifiers.
4.3.2
For linkages within and external to any system the unique identifier is the primary key to managing
audio data and all of its associated files, e.g. the master copies, playback copies, compressed versions
of playback copies, metadata files, edit lists, accompanying texts, images, versions of any one of those
master files or derivatives. Therefore, unless the archive is using a system-assigned ‘dumb’ identifiers,
it is vitally important that the unique identifier’s structure is logically determined, clearly understood
by those who have to apply it, and able to be read by people and machines. It is also important to
reveal the connections between ‘families’ of data files: one commentator likens this connectivity to
“the persistent ‘thread’ that enables resources to be re-tagged or re-stitched on the Web”. Talking in
terms of ‘resources’ rather than collections is an important underlying concept in these guidelines.
4.3.3
One of the most powerful ways of constructing an identification system that reveals those
connections is to base it on the concept of Root ID (RID). The RID is the identifier of entity. All the
files and folders involved in the representation of the entity will be derived from the RID by addition
of prefixes and suffixes such as the creation of unique identifiers.
4.3.4
Regardless of whether identifiers have embedded intelligence or not, it is normal for computergenerated and computer-readable identifiers to have fixed length codes as the primary key. This
offers the following advantages:
4.3.4.1 They enable rules to be established for creating new unique identifiers.
4.3.4.2 They guarantee unambiguous recognition in the system (and for users who know
the rules).
4.3.4.3 They permit validation of the code or components of the code.
4.3.4.4 They support searching, sorting and reporting.
4.3.5
There has been a prolonged debate about the relative merits of dumb and intelligent or expressive
unique identifiers. Most systems allocate a dumb identifier the moment data are saved. They are
quickly applied, require no human intervention and their uniqueness is guaranteed. However, their
randomness and arbitrariness means that other ways have to be found to show how the different
files generated in the life-cycle of a digital resource connect. A better way to do this is by use of
intelligent, expressive identifiers.
4.4
Identifier Characteristics
4.4.1
The following characteristics should be considered when developing a naming scheme:
4.4.1.1 Uniqueness, the naming scheme must be unique within the context of the organisation’s
digital resources and, if necessary, globally unique.
4.4.1.2 There should be a commitment to persistence; an organisation must have a commitment to
maintain the association of the current location of the resource with the persistent identifier.
29
Unique and Persistent Identifiers
4.4.1.3 An identifier system will be more effective if it is able to accommodate the special
requirements of different types of material or collections.
4.4.1.4 Although not absolutely critical, and not essential for machine generated persistent
identifiers, a system will generally be more successful if it is easy to understand and apply,
and if it lends itself to short and easy to use citations.
4.4.1.5 The identifier should be capable of distinguishing parts of an item, as well as versions and
roles that a digital item might have. Relying on the file extension to distinguish a distribution
copy from an archival copy is not advisable as the format may change over time, though the
role remains the same (Dack 1999).
4.4.1.6 The identifier should permit batch renaming for ingestion into different content
management systems.
30
Chapter 5: Signal Extraction from Original Carriers
5.1
Introduction
5.1.1
The first, and most significant part of the digitisation process is the optimisation of signal retrieval
from the original carriers. As a general principle, the originals should always be kept for possible
future re-consultation. However, for two simple, practical reasons any transfer should attempt to
extract the optimal signal from the original. Firstly, the original carrier may deteriorate, and future
replay may not achieve the same quality, or may in fact become impossible, and secondly, signal
extraction is such a time consuming effort that financial considerations call for an optimisation at
the first attempt.
31
Signal Extraction from Original Carriers
5.2 Reproduction of Historical and Obsolete Mechanical Formats
5.2.1 Introduction
5.2.1.1 The first audio recordings made were mechanical recordings, and this approach remained almost
the only viable method for capturing sound until developments in electrical circuitry began to
create a market for magnetic recordings during and after the 1930s. Mechanical recordings are
recognised by the presence of a continuous groove in the surface of the carrier into which the
signal is encoded. The encoding of monophonic audio is achieved either by modulating the bottom
of the groove up and down with respect to the surface (vertical or hill-and-dale recordings), or
from side to side (lateral recordings). All cylinder recording are vertical recordings, as are Edison
Diamond Discs, some early shellacs and discs recorded by Pathé up until about 1927, when they
began to record laterally cut discs. For a time, some radio transcription discs were also vertically cut
recordings, primarily in the US. Lateral cut recordings are the more common form, and most coarse
groove recordings (sometimes called 78s), transcription, and instantaneous discs are lateral, as are
monophonic Long Play (LP) microgroove records. Microgroove discs are discussed separately in
section 5.3.
5.2.1.2 Mechanical sound recording formats are analogue, so called because groove wall is modulated in
a continuous representation of the wave form of the original audio. Almost all of the mechanical
recordings discussed are now obsolete, in that the industry which once created these artefacts no
longer supports them. Early mechanical recordings were acoustic, as the sound waves acted directly on
a lightweight diaphragm which drove the cutter directly into the recording surface. Later mechanical
recordings were “electrical recordings” as they used a microphone and amplifier to drive an electrical
cutting head. From 1925 onwards almost all recording studios began to make electrical recordings.
5.2.1.3 As the early mechanical recordings were all made when the industry was developing, there were
few standards. Those that existed were poorly observed as the technology was constantly evolving,
and many of the manufacturers would keep their latest techniques secret in order to gain a market
advantage. One legacy of this period is the immense degree of variation in most aspects of their
work, not least in the size and shape of the recorded groove (see 5.2.4), recording speed (5.2.5) and
equalisation required (5.2.6). Consequently, there is a need for those working with the recordings
to have specific knowledge about the historical and technical circumstances under which these
recording were created. For obscure or non standard recordings, it is advisable to seek advice from
specialists, and even for the more common types of recording, caution should be exercised.
5.2.2 Selection of Best Copy
5.2.2.1 Mechanical recording may be either instantaneous or replicated. The former are mostly unique
items, single recordings created of a particular event. These include wax cylinders1, lacquer (also
known as acetate) discs and recordings created by office dictation machines (see 5.2.9). Replicated
recordings, on the other hand, are pressed or moulded reproductions of an original master, and are
almost always manufactured in multiples. Instantaneous recordings should be identified and treated
separately and carefully.
5.2.2.2 Instantaneous cylinders may be distinguished by their waxy appearance and feel, and were generally
made of a soft metallic soap. Their colour typically can vary from a light butterscotch to a dark
1 The earliest commercial wax cylinders were replicated acoustically, one from another, and performers would often do multiple
sessions to create batches of similar recordings. They should all be regarded as unique items.
32
chocolate brown, or very rarely, black. Replicated cylinders were made of a much harder metallic
soap, or alternatively of a celluloid sleeve over a plaster core. These were manufactured in a
variety of colours, though black and blue were the more common, and usually bear some content
information embossed into a flattened end.
5.2.2.3 The first disc format capable of instant replay appeared around 1929. The discs were made of
an uncoated soft metal (usually aluminium, possibly copper or zinc) into which a lateral groove
was embossed rather than cut, and are easily distinguished from replicated shellac discs. Like
the subsequent lacquer discs, the embossed metal format was designed to allow the discs to be
replayed on standard gramophones of the time, and so recordings can be loosely categorised as
coarse groove and 78 rpm, but the transfer engineer should expect some variation, not least in the
groove profile.
5.2.2.4 Lacquer or acetate discs, introduced in 1934, are most frequently described as laminated, although
that is not their method of manufacture, or as acetates, which is not the nature of their recording
surface. They most commonly consist of a strong and stiff base (aluminium or glass, occasionally zinc)
covered with a layer of cellulose nitrate lacquer, coloured dark to improve observation of the cutting
process. Rarer are discs which have a cardboard base. The cutting properties are controlled by the
addition of plasticisers (softening agents), such as castor oil or camphor.
5.2.2.5 Lacquer discs can appear similar to shellac or more typically vinyl, but they can be distinguished in
several ways. The base material can often be seen between the outer lacquer layers, either within
the centre hole or at the disc edge. Where the disc has a paper label the content information will
often be typed or handwritten rather than printed. On discs without paper labels one or more
additional off-centre drive holes may be seen near the centre hole. Though cellulose nitrate lacquer
discs on metal or glass base are the most common instantaneous disc, in practice a great variety of
other materials were used, such as cardboard as the base media, or gelatine as the recording surface,
or as a homogenous recording disc.
5.2.2.6 Due to their inherent instability lacquer discs should be transferred with a high priority.
5.2.2.7 The selection of the best copy, in those circumstances where multiple copies on instantaneous discs
exist, is usually a process of determining the most original intact copy of an item. In the case of mass
produced mechanical recordings, where the existence of multiple copies is the normal situation, the
following guide to selection of best copy applies.
5.2.2.8 Selection of the best copy of replicated mechanical media draws on knowledge of the production
of the recording, and the ability to visually recognise wear and damage which would have an audible
effect on the signal. The recording industry uses numbers and codes, generally located in the space
between the run-out groove and the label in a disc recording, to identify the nature of the recording.
This will help the technician determine which recordings are in fact identical, or alternate recordings
of the same material. Visual signs of wear or damage are best seen in the way a recording reflects
light. To best show the effect an incandescent light is a necessity, generally aimed at the recording
from behind the technician’s shoulder, so that they are looking down the beam of light. Fluorescent
tubes, or energy saving compact fluorescent lights do not provide the necessary coherent light
source to reveal wear and should not be used. A stereoscopic microscope is helpful in assessing
groove shape and size, and in examining wear caused by previous replay, which helps selection of the
correct replay stylus. A more objective approach involves using a stereo-microscope with a built-in
reticule which enables more accurate selection of styli (Casey and Gordon 2007).
33
5.2.3 Cleaning and Carrier Restoration
5.2.3.1 Grooved media may be adversely affected by past use, or through natural decomposition of the
constituent materials, hastened to a greater or lesser degree by environmental storage conditions.
Debris including dust and other airborne material can accumulate within the grooves, and fungal
growth may be present where climatic conditions have allowed. This is particularly common with
instantaneous cylinders. In addition, lacquer discs may experience exudation of the plasticisers
from the lacquer itself. This typically has a white or gray mould-like appearance, but is distinguished
by a greasy consistency. Mould, on the other hand, is typified by feathery or thread-like white or
gray growth. Each of these conditions will compromise the ability of the replay stylus to follow the
groove pattern accurately, and so appropriate cleaning of the carrier is necessary.
5.2.3.2 The most appropriate cleaning method will depend on the specific medium and its condition. In
many cases a wet solution will produce the best results, but the choice of solution must be made
carefully, and in certain cases it may be best to avoid the use of any liquids. Record cleaning solutions
which do not disclose their chemical composition should not be used. All decisions about the use of
solvents and other cleaning solutions should only be made by the archivist in consultation with the
appropriate technical advice by qualified plastics conservators or chemists. It can however be stated
that lacquer and shellac discs, and all types of cylinder, should never be exposed to alcohol, which
may have an immediate corrosive effect. Shellac discs frequently contain absorbent fillers which can
expand on sustained contact with moisture, and so should be dried immediately after cleaning with
any wet solution. Any wet cleaning process should avoid contact with paper disc labels.
5.2.3.3 Castor oil has commonly been used as a plasticiser in the production of cellulose nitrate lacquer discs,
which, as it exudes from the disc surface typically breaks down into palmitic and stearic acids. The loss
of plasticiser causes the coating to shrink and consequently crack and peel away from the base. This
is known as delamination. Several solutions have been employed successfully in removing the exuded
acids (see in particular Paton et al 1977; Casey and Gordon 2007, p27). It has been observed however
that after cleaning, lacquer discs may continue to degrade at an accelerated rate. It is sensible therefore
to create digital copies of the material held on cleaned lacquer discs as soon as possible after cleaning.
It must again be stressed that the effect of all solvents should be tested before use. Some early lacquer
discs have a gelatine rather than cellulose nitrate playing surface for example, which is soluble and
would instantly suffer irreversible damage if treated with any liquid solution.
5.2.3.4 Certain other media may not be appropriate for wet cleaning, including shellac and lacquer discs
which were manufactured with paper or card layers beneath the playing surface. Similarly, lacquer
discs displaying cracking or peeling surfaces must be treated with great care, and instantaneous
cylinders should be cleaned with a soft dry brush only, applied along the groove path. However,
where mould spores are thought to be present, the utmost care should be taken to minimise
cross contamination. Special care should be taken when cleaning moulds and spores as these may
cause serious health problems. Operators are strongly advised to obtain professional advice before
commencing work on such infected materials.
5.2.3.5 In cases where wet cleaning is deemed appropriate, it should be carried out with both the solution
and carrier at room temperature, to avoid any damage to the carrier caused by thermal shock.
5.2.3.6 Often the most effective and efficient method of wet cleaning is to use a record cleaning machine
employing a vacuum to remove the waste liquid from within the groove, such as those made by
Keith Monks, Loricraft or Nitty Gritty.
34
5.2.3.7 Particularly dirty carriers, or those with stubborn marks such as dried-on paper deposits, may
be more appropriately cleaned using an ultrasonic bath, into which the carrier (or portion of the
carrier) is placed. The process works by vibrating a solution around the item, loosening dirt deposits.
5.2.3.8 In cases where it is not possible or appropriate to employ such equipment, hand washing may be
carried out using an appropriate short bristled brush. Clean tap water may be used in the washing
process, but should always be followed by a thorough rinse in demineralised water to remove any
consequent contamination.
5.2.3.9 In addition to cleaning, some further form of restoration may be required. Shellac discs and cylinders
of all types are brittle and liable to break if mishandled, and shellac will melt and warp at high
temperatures. The exudation of plasticiser from lacquer discs causes the lacquer layer to contract
upon a stable metal or glass base, creating stresses between the layers and resulting in cracking
and peeling of the lacquer playing surface. Reconstruction of broken discs and cylinders is ideally
done without resorting to glues or adhesives, as these inevitably form a barrier between the parts
being joined which, however small, will be audible. Such processes are also generally irreversible,
allowing for no second chances. The manufacturing processes used in replicating both shellac discs
and cylinders will often result in a degree of internal stress in the carrier. If broken, the divergent
stresses in the constituent pieces may cause them to contort somewhat. To minimise the effect of
this, broken carriers should be reconstructed and transferred as soon as possible after the breakage
occurs. The individual parts of broken carriers should be stored without touching. Storing them
unsecured in their reconstructed form may encourage the finely detailed broken edges to rub
together, causing further damage.
5.2.3.10 Shellac discs are usually best reconstructed on a turntable, upon a flat platter larger than the disc
itself (another, disposable or non-archival disc is often ideal). The pieces are placed upon it in their
correct positions and held in place around the centre spindle with re-usable pressure sensitive
adhesive putty such as Blu-Tack, U-Tack, or similar around the outside of the disc. Where discs are
thinner around the edge than in the middle, the putty may be used to raise the edges to the correct
height. Take note of the direction through the groove that the stylus will travel: where the pieces
cannot be perfectly vertically aligned, it is better for both the stylus and the resulting transfer that
the stylus be obliged to drop down onto a lower fragment rather than be pushed up abruptly onto
a higher one.
5.2.3.11 Cylinders which have suffered a neat break can often be reconstructed around the playback
mandrel using ¼ inch splicing tape as a form of bandage. More complex breakages will require
specialist help.
5.2.3.12 Flakes from peeling lacquer disc surfaces may be temporarily fixed to allow the disc to be played,
using tiny amounts of petroleum jelly between the flake and disc base. The long term effects of this
procedure are likely to be deleterious, and it is used to attempt replay of discs which are judged to
be unplayable by any other currently practicable means.
5.2.3.13 Where it is possible to play a warped or bent disc without flattening it, this should be the preferred
option, as the risks associated with disc flattening described below will attest. The ability to play a
warped disc can often improve when the rotational speed of the disc is reduced (see 5.2.5.4).
5.2.3.14 Shellac discs may be flattened in a laboratory (i.e., non-domestic) fan-assisted oven. The disc should
be placed on a sheet of pre-heated toughened glass, and it is imperative that both disc and glass be
clean, to prevent dirt fusing with the disc surface. There is a danger that in curing vertical warpage,
35
some lateral warpage may occur. The disc should therefore not be heated any more than it has to
be, and a temperature of around 42C is often sufficient (Copeland 2008 Appendix 1).
5.2.3.15 Flattening discs is a useful process because it can make unplayable discs playable. However, current
research into the procedure of flattening discs with heat shows that it causes a measurable rise in
subsonic frequencies, even in the low audible frequency range (Enke 2007). Though the research is
not conclusive the point should be noted in determining whether to flatten a particular disc. The
analysis of the affect of flattening was carried out on vinyl discs and whether it applies to shellac is
yet to be determined, though the lower temperatures associated with treating shellac make it much
less of a risk. Nonetheless, the possibility of such damage has to be weighed against enabling the
playing of the disc.
5.2.3.16 Though it is strongly advised not to attempt to permanently flatten an instantaneous disc (and any
attempt is likely to be unsuccessful and damage the disc surface), in some instances the warpage
may be temporarily reduced by clamping or otherwise fixing the disc edges to the turntable. Great
care must be taken, especially with lacquer discs whose surface may be damaged if placed under
stress. Laminated flexible discs with a warp may have been rendered flat by placing the disc on the
vacuum platter of a disc cutting lathe and carefully bringing the disc flat. All physical treatment should
be undertaken with great care to avoid damage.
5.2.3.17 Some replicated discs have been produced with a non-centric spindle hole. It is preferable to
play such discs on a turntable with a removable spindle or to raise the height of the disc above
the spindle using, for example, waste discs and rubber interleave. In the latter case the height of
the pickup arm should be raised at the supporting column by the same amount. It is possible to
re-centre the hole using a reamer or drill, but such invasive approaches should be undertaken
cautiously and never with unique or single copies. Altering the original artefact may well result in loss
of secondary information.
5.2.4 Replay Equipment
5.2.4.1 Grooved recordings were made to be replayed with a stylus and pickup. Though optical technology
has some special advantages which are discussed below (see section 5.2.4.14), and though advances
in optical replay are bringing closer the likelihood of a practical system which does not require
physical contact, currently the best and most cost effective approach to retrieving the audio content
from such a recording is with the correct stylus. For lateral recordings a set of styli with different
radii in the range of 38 µm (1.5 mil2), to 102 µm (4 mil), with an additional focus on 76 µm
(3 mil) and 65 µm (2.6 mil) for early and late electrics respectively, is essential. The correct stylus for
the particular groove will ensure best possible replay by fitting properly into the replay area, and
avoiding worn or damaged sections of the groove wall. Records in good condition will reproduce
with greater accuracy and reduced surface noise with elliptical tips; records in visually poor condition
may be better suited to conical tips. Wear from previous use may well be to a particular region of
the groove wall leaving some undamaged areas. Choosing an appropriate tip size and shape will
allow these undamaged sections to be reproduced without including distortions caused by the
damaged sections. A truncated stylus of either shape will better avoid any damaged areas in the
bottom of the groove. Care should be taken in the replay of Pathé lateral discs as they typically have
a larger groove width, and may require larger tip radii to avoid damage to the groove bottom.
2 1 mil is .001" (1,000th of an inch).
36
5.2.4.2 Mono pickups are available, but it is more common to use stereo pickups as these allow separate
capture of each groove wall. Moving coil pickups are often highly regarded because of their
enhanced impulse response which aids in improving the separation of groove noise from audio
signal. However, the range of various tip sizes for moving coil pickups is not as wide as that for
moving magnet, are integral to the pickup, and those that can be ordered are around four time
more expensive. Moving magnet pick ups are more common, more robust, lower cost, and generally
more than adequate for the task. When replaying shellac discs a tracking force in the range of
30–50mN (3–5 grams) is often appropriate. It is recommended that a lesser tracking force be
applied to lacquer discs. An advantage in using a stereo pickup is that this allows the two resultant
channels to be stored separately, enabling future selection or processing of the separate channels.
For listening the two channels may be combined in phase for a lateral recording, and out of phase
(with respect to the pickup) for a vertical recording.
5.2.4.3 Selection of a suitable stylus in vertical recordings is governed by different criteria to lateral
recordings. Rather than choosing a stylus to sit in a particular space on the side of a groove wall,
playback of cylinders and other vertical cut recordings requires that a stylus be chosen that is a best
match for the bottom of the groove. This is critical with instantaneous cylinders, where even very
light tracking forces will cause damage if the incorrect stylus is chosen. A spherical stylus is generally
preferred especially if the surface is damaged, though an elliptical stylus may well avoid frequency
dependent tracking error. Typical sizes are between 230 (9 mil) and 300 µm (11.8 mil) for standard
cylinders (100 grooves/inch) and between 115 (4.5 mil) and 150 µm (5.9 mil) for 200 grooves/inch
cylinders. Cylinders should be replayed with a stylus whose tip has a radius a little smaller than the
bottom radius of the groove. A truncated stylus will damage the groove because tracking will take
place at the edge rather than the tip, resulting in increased pressure to that part of the groove.
5.2.4.4 When it comes to making decisions about what equipment to acquire, knowledge of the content
of a particular collection will be the primary guide to determining the type of equipment required.
Different types of carriers will obviously require different types of replay equipment, but even within
similar carriers some specialist needs may arise.
5.2.4.5 Generally, historical equipment should not be used, mainly because of its poor rumble performance
and in the case of cylinder players, greatly increased tracking force compared with equivalent
modern replay equipment. Some problematic cylinders may not be playable on this type of
equipment as modern cylinder players normally track the grooves with auto-controlled feed
retrieved from the motion of the needle. When using this set up it is virtually impossible to properly
track locked grooves, or scratches nearly parallel to the groove. This problem can be solved by using
a modern player with fixed feed, or a modified historical cylinder player.
5.2.4.6 Radio transcription discs commonly have a diameter of 16 inches. If such discs are held in a
collection, it will be necessary to procure a turntable, arm and pickup for discs of this size. For
standard discs up to 12 inch records generally a modern precision turntable, modified to allow
varispeed in a wide range, is required.
5.2.4.7 Negative metal stampers manufactured for mass replication of discs can themselves be replayed if
an appropriate bi-point or stirrup stylus is available. This type of stylus sits astride the ridge (which
is a negative impression of a disc groove) and needs to be placed carefully so as to avoid falling
between adjacent ridges. As the stamper holds an inverse spiral to the discs it was designed to
replicate, it should revolve anticlockwise, that is, in the opposite direction to a replicated disc, in
37
order to be played from start to finish. To do this correctly would require a fully reverse-mounted
tone arm. Much simpler and just as effective would be to play the stamper from finish to start on a
standard clockwise turntable, and reverse the resulting digital transfer, using any current high quality
audio editing software.
5.2.4.8 Bi-point styli are now extremely difficult to obtain, and fall into two categories, namely low- and
high-compliance. The former are designed to repair manufacturing defects in metal stampers and
as such are not ideally suited to archival transfer work. The latter, employing a significantly lighter
tracking force are designed for audible replay rather than physical modification of the stamper, and
so can be considered more suitable.
5.2.4.9 Turntables and cylinder phonographs for archival transfer purposes need to be precision mechanical
devices in order to produce the minimum transmission of spurious vibrations to the record surface,
which acts as a receiving diaphragm for the pickup. Low frequency vibrations are called rumble, and
these vibrations frequently have a considerable vertical component. To reduce rumble generated by
external vibrations,the replay apparatus must be placed on a stable foundation that is not likely to
transmit structural vibrations. The replay machine should have a speed accuracy of at least
0.1 per cent; wow and flutter (DIN 45 507 weighted) better than 0.01 per cent; and an unweighted
rumble of better than 50 dB. The turntable will be either belt or direct drive; friction drive wheel
machines are not recommended as suitable speed accuracy and low rumble is not possible with
these devices.
5.2.4.10Any power supply wiring and the electric motor must be shielded to prevent injection of electrical
noises into the pickup circuit. If required, additional Mu-Metal plates may be used to shield the
motor from the pickup. The connecting cable to the pre-amplifier must be within the specifications
regarding the loading impedance for the pickup. The installation should follow best analogue practice
and adequate grounding procedures must be adhered to in order to ensure noise is not added to
the audio signal. All of the above suggestions and specifications should be quantified, by analysing the
output from test discs (see 5.2.8).
5.2.4.11Both turntables and cylinder phonographs should be capable of variable replay speed, with the
possibility of half-speed replay being particularly desirable (see 5.2.5.4), and feature a speed readout
to allow documentation, possibly as a signal suitable for automatic logging for metadata. The pickup
arm must sit on a base that can be adjusted, not only as regards distance from the turntable centre,
but also in elevation.
5.2.4.12In order to evaluate and decide on the most appropriate equipment and settings, comparisons
must be made between the different options. This is best achieved through simultaneous, or A/B
comparison, and audio editing software should be chosen which allows multiple audio files to
be compared simultaneously. Transferring portions of a recording with different parameters and
aligning the different resulting audio files in the editor for listening purposes, allows repeated direct
comparison and reduces the inherent subjectivity of the process to a minimum.
5.2.4.13A decision will need to be made as to the application of an equalisation curve prior to digitisation
(see 5.2.6 Replay Equalisation). Where this is desirable, an appropriate preamplifier will be required,
adjustable to recreate all necessary settings.
5.2.4.14As an alternative to contact pickups the entire surface of a disc or a cylinder can be scanned or
photographed at high resolution then converted to sound. Various projects have been developed up to
a (quasi-) commercial level (ELP Laser Turntable; IRENE by Carl Haber, Vitaliy Fadeyev et al; VisualAudio
by Ottar Johnsen, Stefano S. Cavaglieri, et al, Sound Archive Project, P. J. Boltryk, J. W. McBride, M. Hill,
38
A. J. Nascè, Z. Zhao, and C. Maul). However, all of the techniques investigated so far present some
limits (optical resolution, image processing, etc.), resulting in poor sound quality, if compared to using
standard mechanical devices. A typical application for optical retrieval technology is for records in
very bad condition, where mechanical replay devices would fail, or where the recordings are so
fragile that the replay process would cause unacceptable damage.
5.2.5 Speed
5.2.5.1 Despite being referred to as “78s”, it was very often the case that coarse groove shellac discs were
not recorded at precisely 78rpm, and this is especially the case with recordings made prior to the
mid-1920s. At different times certain recording companies would set different official speeds, and
even these were varied by recording engineers, on occasion during recording sessions. There is
insufficient space here to discuss specific settings, though they are covered elsewhere in detail (see
for example Copeland 2008, Chapter 5).
5.2.5.2 It is imperative that the disc be replayed for transfer as close to the original recording speed as is
possible, in order to recapture the sound event originally recorded as faithfully and objectively as
possible. However, subjective decisions often have to be made, and to this end knowledge of the
recorded content or context in which the recording was made can be useful. The chosen replay
speed should be documented in accompanying metadata. This is particularly important where any
doubt remains as to the actual recording speed.
5.2.5.3 Recording speeds of commercial replicated cylinders standardised at 160rpm around 1902, although
prior to that Edison, at least, applied several short-lived speed standards (all lower than 160 rpm;
see Copeland 2008, Chapter 5). Instantaneous cylinders, while often recorded around 160 rpm or
so, have been found with recording speeds ranging from below 50 rpm to over 300 rpm. In the
absence of a recorded reference pitch (as provided occasionally by some early recordists) these will
need to be set by ear, and documented accordingly.
5.2.5.4 Replaying a disc or cylinder at reduced speed may improve the ability to accurately track damaged
carriers. There are many ways that this can be attempted depending on the equipment available,
but attention should always be paid to the effect this will have on the sample rate of the digital file
when adjusted to compensate for the change, and an appropriate sample rate should be chosen
accordingly. Half-speed replay may be the simplest to employ, as it can be coupled with a doubled
sample rate to produce corrected-speed transfers with a minimum of distortion caused by sample
rate conversion. It should be noted that reduced speed playback is just one of many techniques that
may be used to solve tracking problems. It is useful to try other procedures first such as adjusting
the anti-skate to counter-balance the direction that the stylus jumps from a skip or using more or
less tracking force to keep the stylus in the grooves.
5.2.5.5 Although playback with reduced speed may deliver increased surface noise compared with original
speed, it is also the case that the action of filtering equipment, digital or otherwise, may be more
effective. Playing at reduced speed means that the high frequency signal is halved in frequency, while
the rise time of the unwanted impulse noise caused by surface damage remains the same and
can be more easily distinguished from each other. However, some sophisticated predictive filtering
equipment may be less effective at non-original speeds. Low speed copies must be flat transfers,
without applied equalisation which can be introduced later (see 5.2.6).
39
5.2.6 Replay equalisation
5.2.6.1 Equalisation became a possibility with the introduction of electrical recordings; it also became a
necessity. Equalisation in recording is the application of a frequency dependant boost or cut to the
signal before it is recorded, and the inverse cut or boost on replay. This became a possibility with
electrical recordings because the recording and replay systems now included electrical circuitry
which enabled a process which could not have been applied in the acoustic recording process. It
became a necessity because the way sound is represented on a disc would not allow the dynamic
range or frequency response that the electrical technology enabled, to be recorded otherwise.
5.2.6.2 Sound can be recorded on a disc in two different ways; “constant velocity” or “constant amplitude”.
Constant velocity on a disc is when the transverse speed of the stylus remains constant regardless
of the frequency. An ideal acoustic disc recording would display constant velocity characteristics
throughout its recordable range. One of the implications of constant velocity is that the peak
amplitude of the signal is inversely proportional to the frequency of that signal, which means
that high frequencies are recorded with small amplitudes, and low frequencies are recorded with
comparatively large amplitudes. The difference in amplitude can be very marked; across 8 octaves,
for example, the ratio in amplitude between the lowest and highest frequency is 256:1. At low
frequencies, constant velocity is unsuitable as the excursion of the groove becomes excessive,
reducing the amount of available recording space, or causing cross over between tracks.
5.2.6.3 Constant amplitude, on the other hand, is when the amplitude remains constant regardless of the
frequency. Constant amplitude, while most suitable for low frequencies, is unsuitable for higher
frequencies as the transverse velocity of the recording or replay stylus could become so excessive as
to cause distortion. To overcome the dilemma caused by both these approaches, disc manufacturers
recorded electrical discs with more or less constant amplitude at the lower frequencies and
constant velocity at the higher frequencies. The point of change between the two is described as the
low frequency turnover (see table 5.2).
5.2.6.4 As the recording technology improved and increasingly higher frequencies could be captured, these
higher frequencies resulted in correspondingly smaller amplitudes on the disc. A consequence of
the very small amplitude of these high frequency components is that the ratio of the signal to the
irregularity in the surface of the disc approaches equivalence. This would mean that the very high
frequencies would be comparable in amplitude to the unwanted surface noise, otherwise known
as a poor signal to noise ratio. To overcome this, the disc manufacturers began to boost the higher
frequency signals so that these very high frequencies were often, though not always, constant
amplitude recordings. The point at which the higher frequencies are switched from constant velocity
to constant amplitude is called HF Roll-off Turnover (see table 5.2). The function of this higher
frequency equalisation is improvement in the signal to noise ratio, and it is commonly termed preemphasis in recording and de-emphasis in replay.
5.2.6.5 The commonly used dynamic or magnetic pick-ups are velocity transducers, and their output can be
directly fed into a standard preamplifier, if that is desired. Piezo-electrical and optical replay systems
are amplitude transducers. In these cases a general 6dB/octave slope equalisation must be applied as
the difference between a constant velocity and constant amplitude recording is 6dB per octave.
5.2.6.6 Acoustically recorded discs have no intentionally applied equalisation in recording (though engineers
were known to adjust parts of the recording path). As a consequence of the recording process,
the spectra of an acoustic disc would display resonant peaks in amplitude and related lows.
40
Applying a standard equalisation to compensate for the acoustic recording process is not possible
as resonances in the recording horn and the stylus diaphragm, not to mention other mechanical
damping effects, can vary between recordings, even recordings from the same session. In such cases
the recordings should be replayed flat, i.e. without equalisation, and equalisation should be applied
after the transfer has been made.
5.2.6.7 With electrical recordings it is necessary to decide whether to apply an equalisation curve on replay,
or to transfer flat. Where the curve is accurately known equalisation may be applied either at the
preamplifier prior to making the copy, or applied digitally after making a flat copy. Where doubt remains
as to the correct equalisation curve, a flat transfer should be made. Subsequent digital versions may
employ whichever curve seems most appropriate, so long as the process is fully documented, and the
flat transfer retained as the archival master file. Whether or not equalisation is applied during the initial
transfer, it is imperative that noise and distortion from the analogue signal chain (everything between
the stylus and analogue-to-digital converter) is kept to an absolute minimum.
5.2.6.8 It is worth noting that a flat transfer will require around 20dB more headroom than one where
an equalisation curve has been applied. However, as the potential dynamic range of a 24 bit digital
to analogue convertor exceeds that of the original recording, the extra 20dB headroom can be
accommodated.
5.2.6.9 Apart from the dynamic range limitations mentioned above, a drawback with transferring
electrically recorded discs without de-emphasis is that stylus selection is primarily made through
aural assessment of the effectiveness of each styli, and it is more difficult, though not impossible,
to make reasonable assessment of the effect of different styli while listening to unequalised audio.
An approach taken by some archives is to apply a standard, or house, curve to all recordings of a
particular type in order to make stylus selection and other adjustments, and subsequently produce
a simultaneous flat and equalised digital copy of the audio. As the exact equalisation is not always
known, a flat3 copy has the advantage of allowing future users to apply equalisation as required, and
is the preferred approach.
5.2.6.10There is some debate as to whether noise reduction tools for the removal of audible clicks, hiss
etc are more effective when used before an equalisation curve is applied rather than afterwards.
The answer very likely varies according to the specific choice of tool and the nature of the job to
which it is applied, and in any event will be subject to change as tools continue to evolve. The most
important point in this regard is that noise reduction equipment, even fully automated tools with no
user-definable parameters, ultimately employs subjective and irreversible processes, and so should
not be used in the creation of archival master files.
5.2.6.11A complete record of all decisions made, including choice of equipment, stylus, arm, and equalisation
curve (or its absence) must be recorded and maintained in metadata.
5.2.6.12The main equalisation curves for replay are listed below.
3 Flat is generally taken to mean the unequalised output from a velocity type pickup.
41
Equalisation Chart for
Electrically recorded coarse
groove (78 rpm) Discs
Acoustics
Brunswick
Capitol (1942)
Columbia (1925)
Columbia (1938)
Columbia (Eng.)
Decca (1934)
Decca FFRR (1949)
early 78s (mid-’30s)
EMI (1931)
HMV (1931)
London FFRR (1949)
Mercury
MGM
Parlophone
Victor (1925)
Victor (1938–47)
Victor (1947–52)
LF Turnover4
HF Roll-off Turnover
(-6 dB/octave,
except where marked)
0
500 Hz (NAB)
400 Hz (AES)
200 Hz (250)
300 Hz (250)
250 Hz
400 Hz (AES)
250 Hz
500 Hz (NAB)
250 Hz
250 Hz
250 Hz
400 Hz (AES)
500 Hz (RIAA)
500 Hz (NAB)
200–500 Hz
500 Hz (NAB)
500 Hz (NAB)
2500 Hz
†
5500 Hz (5200)
1590 Hz
2500 Hz
3000 Hz*
3000 Hz*
2500 Hz
2500 Hz
5500 Hz (5200)
5500 Hz (5200)
2120 Hz
†
†
Roll-off @
10 kHz
0 dB
0 dB
-12 dB
-7 dB (-8.5)
-16 dB
0 dB
-12 dB
-5 dB
0 dB
0 dB
0 dB
-5 dB
-12 dB
-12 dB
0 dB
-7 dB (-8.5)
-7 dB (-8.5)
-12 dB
Table 1 Section 5.2 Equalisation Chart for Electrically Recorded Coarse Groove (78 rpm) Discs5.
* 3 dB/octave slope. N.B. A 6 dB/octave slope should not be used on these marked frequencies because though it may be adjusted
to give the correct reading at 10kHz, rolloff would commence at the wrong frequency (6800 Hz) and be incorrect at all other
frequencies.
† This only a recommended roll-off in order to achieve a more natural sound. The pronounced HF content is probably due to
resonant peaks of the microphone and not due to the recording characteristic.
5.2.7 Corrections for Errors Caused by Misaligned Recording Equipment
5.2.7.1 Any misalignment in the cutting stylus should ideally be replicated in the alignment of the replay
stylus, in order to follow the cutter movement as closely as possible, and so capture as much
information from the groove as accurately as possible. There are several ways in which a cutter may
have been misaligned, most of which are difficult to identify, quantify and correct. However the most
common misalignment is somewhat easier to identify and deal with. This occurs when a flat cutter
has been mounted off its major axis, resulting in a recording which, when played with an
on-axis elliptical stylus, reproduces a delay between channels. If the elliptical stylus cannot be rotated
to match the cutter angle, (by appropriately mounting the pick up), replay using a conical stylus
4
See Table 2, Section 5.3, footnote 5 for definitions of “Turnover“ and “Rolloff“.
5
Ref: Heinz O. Graumann:Schallplatten-Schneidkennlinien und ihre Entzerrung, (Gramophone Disc-Recording Characteristics and
their Equalizations) Funkschau 1958/Heft 15/705-707. The table does not include every curve ever used, and other reputable
sources vary slightly in their description of some of those listed. Research in this area is ongoing, and readers may wish to compare
with other findings, such as Powell & Stehle 1993 or Copeland 2008, Chapter 6 etc.
42
may ameliorate the problem to some extent, though with a possible compromise in high frequency
response. Otherwise the delay may be fixed later in the digital domain, subsequent to the initial
archival transfer.
5.2.8 Calibration Discs
5.2.8.1 Calibrating an audio system involves applying a defined input and measuring the corresponding
output over a range of frequencies. A pre-amplifier/equaliser may be calibrated by supplying the
input with a constant signal of variable frequency while loaded with the correct impedance, and
the measurement consists in plotting (or data-logging) the output against frequency. Automatic
apparatus exists for this. In use the input comes from a pickup cartridge, a transducer that converts
a mechanical input to electrical output, and for this we need a mechanical calibrating signal. When
mechanical recordings were commercially available test discs were produced for this purpose. The
Audio Engineering Society (AES), via its Standardisation Committee, runs an ongoing and active
project of developing and publishing a series of simple test discs, both for coarse groove work and
for microgroove. The AES 78 rpm Calibration Disc Set: “Calibration Disc Set for 78 rpm CoarseGroove Reproducers. AES Cat. No. AES-S001-064” is available from the AES website. http://www.
aes.org/standards/b_data/x064-content.cfm
5.2.8.2 If the calibration by means of a test disc has been performed with sufficient resolution, the plotted
curve may be regarded as a plot of the transfer function of the pickup or the pickup-preamplifierequalizer combination. Apart from the fact that visual inspection of the curve will tell the operator
of gross deficiencies, it may actually form the basis of a digital filter that may filter the digitised signal
from the mechanical record, so that it becomes independent of the actual pickup (and preamplifier
and equaliser) used. All it takes is to be certain that no adjustment has been changed between using
the test disc and the mechanical record to be transferred (and ideally that the record materials for
those two inputs behave the same way). (For further discussion see Brock-Nannestad 2000).
5.2.9 Office Dictation Systems
5.2.9.1 Sound recording technology has been marketed and used as a business tool virtually since its
inception. Three broad categories of mechanical dictation formats can be defined, namely cylinders,
discs and belts (see 5.4.15 for magnetic dictation formats).
5.2.9.2 Early cylinders and recording equipment sold for office use were generally the same as those used
for other purposes, the resultant recordings being on standard 105 mm (4 1/8”) length cylinders (see
5.2.4.3). However cylinder formats designed specifically for office use were made for many years
by both Columbia (later Dictaphone) and Edison, both producing cylinders approximately 155 mm
(6 1/8 inch) long with 160 and 150 grooves/inch respectively (Klinger 2002). Some later cylinder
dictation machines recorded electrically rather than acoustically, but little if anything is known today
about pre-emphasis applied.
5.2.9.3 Various grooved disc formats were launched, mostly after World War II, including the Edison
Voicewriter and the Gray Audograph. While many such formats require specialist replay equipment,
seven inch flexible Edison Voicewriter discs may be replayed on a standard turntable employing a
US-type spindle adaptor and microgroove stylus. Recording speeds for these were generally below
33 1/3 rpm.
5.2.9.4 Beginning in the 1940s, several belt recording formats appeared. These were essentially flexible
plastic cylinders, fitted over a twin drum assembly for recording and playback. Perhaps the best
known of these is the Dictaphone Dictabelt. Their flexibility allowed them to be flattened for
43
storage and delivery much like other office stationery, but this often resulted in their becoming
permanently creased, creating challenges for the replay engineer. Carefully and gently raising the
temperature of the belt and replay equipment has been known to be effective in this regard, though
how appropriate this is will depend on, among other things, the particular plastic used in the belt.
Specialist replay equipment will be required to replay belt formats.
5.2.10 Time Factor
5.2.10.1A complex transfer may easily take 20 hours for 3 minutes of sound (a ratio of 400:1). An average
transfer may take 45 minutes for 3 minutes of sound (a ratio of 15:1), which represents time spent
on finding the correct settings for the equipment and choice of stylus, based on an analysis of the
recording as it relates to others of its time and storage history. Some experienced archives suggest
that, for the transfer of unbroken cylinders in average condition, two technical staff, (one expert and
one assistant) can transfer 100 cylinders per week (a ratio of about 16:1). Obviously experience will
improve both the ratio and the ability to estimate time required.
5.2.10.2Digitisation can seem expensive and labour intensive, requiring a great deal of equipment, expertise
and man-hours to transfer audio and create all necessary metadata. However this initial frontloading of effort and resources will be offset by the long-term benefits and savings of retaining a
well-managed digital mass storage repository, greatly reducing future costs of access, duplication and
migration. Note that a crucial factor here is the maintenance of the repository, discussed in detail in
chapter 6 and elsewhere. The extraction of the optimum signal from the original carrier, as defined
in this chapter, is a vital component of this strategy.
44
5.3 Reproduction of Microgroove1 LP Records
5.3.1 Introduction
5.3.1.1 Long Play (LP) microgroove records first made their appearance around 1948, pressed in flexible
vinyl2 and hailed as ‘unbreakable’ in comparison to the preceding commercial records pressed from a
rigid (and easily broken) shellac base.
5.3.1.2 By the time the vinyl disc was developed there was a greater industry agreement on standards.
Grooves were cut at 300–400 to the inch as opposed to the 100 or so grooves per inch that was
characteristic of the shellac pressings, and with a standard sized and shaped stylus on a cutting lathe
that revolved at a speed of 33 1/3 rpm. 7” vinyl records, both singles and ‘Extended Play’ (EP), were
made to be replayed at 45 rpm and in some cases 33 1/3 rpm. Larger diameter discs were on rare
occasions produced for replay at 16 2/3 rpm for speech, where up to 60 mins could be recorded
on one side. Equalisation characteristics still varied between companies, (see Table 2 Section 5.3
Equalisation Chart for Pre-1955 LP Records) however, many preamps catered for these variations.
Eventually agreement was reached and the RIAA (Record Industry Association of America) curve
became standardised throughout the industry.
5.3.1.3 Stereo records were commercially available from around 1958, and initially many records were
produced in both mono and stereo versions. The groove walls are at right angles to each other and
inclined by 45° to the vertical. The inner wall of the groove contains the left channel information, and
the outer groove the right channel information recorded perpendicular to the respective groove
wall. This has remained the standard, although at the time of its introduction a small number of
stereo discs were made with a combination of lateral and vertical technology, an approach that was
soon discontinued. Stereo pick-ups may be used to play mono records, but playing a stereo record
with a mono pick-up will cause severe groove damage.
5.3.2.1 As with historical mechanical and other obsolete formats (see Section 5.2.2 Selection of best copy)
selection is primarily made visually, for speed and to prevent wear. Staff should be well versed in the
codes and identifiers used by the various record companies and usually placed just outside the label.
This may reveal alternative or later takes, remasterings, or pressings. In selecting the best copies for
digitisation, co-operation with other collections should be considered.
5.3.2.2 The working space must make parallel, oblique light available as overhead fluorescent lighting may
obscure evidence of wear. The quality of light must be such that it is very clear what constitutes
merely heavy modulation and what constitutes wear. If two copies only exist, and they display
different wear characteristics, then retain both and transfer both.
5.3.3.1 LPs should be handled very carefully, never allowing fingers to touch the groove area of any vinyl
disc. Sweat and other skin borne deposits may in themselves cause replay noise, however they will
also attract and adhere dust to the surface and enable the growth of moulds and fungi increasing
replay noise. Cotton gloves should be worn when handling discs. If appropriate gloves are not
practical, discs should be withdrawn from (and replaced in) their sleeves in a manner that ensures
1 As some late generation coarse groove recording were pressed in vinyl the use of the term “microgroove” is preferred to using
“vinyl” as a collective description.
2 “Vinyl” is a colloquial term for the material of the discs which basically consists of a polyvinyl chloride / polyvinyl acetate co-polymer
(PVC/PVA).
45
the finger tips are placed on the label area and the base of the thumb at the edge, leaving the
groove area untouched.
5.3.3.2 Dust, the enemy of all sound recordings, is a major problem with LPs for two reasons. The finer
groove means dust particles are comparable in size with the stylus and cause clicks and pops.
The electrostatic nature of vinyl increases the attraction of dust to the surface of the disc. Various
commercial devices have been developed in an attempt to neutralise these static charges, from
carbon-fibre brushes to piezo-electric ‘guns’ that ‘fire’ a neutralizing charge at the record surface, all
of which are effective to varying degrees.
5.3.3.3 The most effective way of cleaning records is to wash them. Cleaning machines, such as the well
known Keith Monks machine, coat the surface with a cleansing fluid which is then removed by a
tracking suction device which moves across the surface to suck up both the fluid and any dust or
dirt in the grooves. A simpler method is washing, avoiding the label area, with demineralised water
and a mild detergent or non-ionic wetting agent such as diluted (1 per cent) Cetrimide (n-cetyl
pyridinium chloride) which has anti-fungal and anti-bacterial properties. The disc may then be
brushed in a circular motion with a soft camel hair paint brush, again avoiding the label area, and
rinsing off, once more using distilled water. Greasy deposits on vinyl discs may be removed with
isopropyl alcohol. As non-vinyl discs may be affected by alcohol, care should be taken to ensure that
the solvent does not cause damage to the disc.
5.3.3.4 Record cleaning solutions which do not disclose their chemical composition should not be used. All
decisions about the use of solvents and other cleaning solutions should only be made by the archivist
in consultation with the appropriate technical advice by qualified plastics conservators or chemists.
5.3.3.5 As with historical mechanical and other obsolete formats (see 5.2.3 Cleaning and Carrier Restoration),
ultrasonic cleaning may be effective. Care should be taken in the selection of solvent, though a
1 per cent solution of Cetrimide in distilled water is an appropriate cleaning solution. The label should
be kept clear of the fluid, and the disc rotated slowly until the whole groove area has been wetted.
5.3.3.6 Perhaps the most effective method of reducing the effects of dirt, dust, and static charge is to play
the records wet. This may be achieved by simply covering the disc with a Cetrimide solution, or
by tracking a soft wet brush ahead of the stylus. Wetting the record can dramatically reduce the
incidence of clicks and pops, however, it has the effect of increasing surface noise in all subsequent
‘dry’ plays. Wet playing using liquids containing alcohol is not recommended as the polymer bearings
of cantilevers may chemically react with negative results.
5.3.3.7 The most frequently needed restoration of a disc recording is flattening. The following approach
applies whether the disc is dish-shaped or bent. A thermostatic oven (a laboratory style oven is
mandatory, a domestic oven is not appropriate) is required at a setting usually not exceeding
55ºC and provided with two very clean sheets of hardened and polished glass, thickness 7 mm,
350 mm square. After hand cleaning and drying the record it is placed on the pre-heated bottom
sheet in the oven and the top sheet is suspended in the oven. After ca. ½ hour the record is
inspected and may well have sunk to a flat position. If not, the elasticity is tested as an indication
of softening, and experience will tell if placing the hot top plate on the record might have the
desired effect. The sandwich is left for ½ hour, and the top sheet is lifted using gloves. If the record
is perfectly flat, the complete sandwich is removed from the oven and left to cool on an insulating
support. If flattening has not been obtained, the temperature is raised in 5ºC intervals and the
procedure repeated. Never apply the flattening force unless the softening is sufficient.
5.3.3.8 Flattening discs is a useful process because it can make unplayable discs playable; however, current
research into the procedure of flattening discs with heat shows that it causes a measurable rise in
46
subsonic frequencies, and even in the low audible frequency range (Enke 2007). Though the research
is not conclusive the point should be noted in determining whether to flatten a particular disc.
The analysis of the affect of flattening was carried out on vinyl discs but the range of tests were
not extensive and further research is required. The possibility of such damage should be weighed
against the benefit of enabling the playing of the disc.
5.3.4.1 Optical replay is available for LPs and should be investigated before selecting any transfer equipment,
however contact transducers, or styli, are presently more common, perceived as less complicated
and preferred by most technicians. When using contact transducers there are so many variables in
the reproduction chain that exact repeatability of any particular replay is not possible. Pick-up arm,
cartridge, stylus, tracking force, previous groove deformation or wear all contribute to the variability
in replay. Even temperature can affect the replay characteristics of a cartridge/stylus combination
to some degree. However, if LPs are to be captured for digitisation high quality components in the
playback chain from stylus to recording equipment will ensure the most accurate audio capture.
5.3.4.2 Perhaps the most important part of the replay chain is the cartridge/stylus combination. Moving coil
pickups, considered by some to be the most sensitive, tend to have a price tag and lack of robustness
that precludes their use for anything but very careful domestic use. A good, high compliance, low
tracking force (less than 15 mN, commonly quoted as 1.5 grams) variable reluctance (moving magnet)
cartridge with a bi-radial (“elliptical”) stylus will be the most practical choice. Replay styli should include
a range from 25 µm (1 mil), commonly used on early mono LPs, to 15 µm (0.6 mil), including conical,
elliptical and truncated styli depending on the age and condition of discs to be played.
5.3.4.3 Attention should be given to the adjustment of vertical tracking angle (VTA) of the pickup system,
which ideally should match the VTA produced in the recording process. The recommended playback
VTA during the 1960s was 15±5°, which changed by 1972 to 20°±5°. It is impossible, however,
to check the VTA of a given record (unless with test records which permit the evaluation of the
intermodulation distortion of a vertical signal). As a basic adjustment, however, attention should
be given to the horizontal position of tone arm, parallel to the surface of the record, under the
appropriate tracking force. This should ensure the VTA intended by the pick-up system manufacturer.
Any deviation from there can be achieved by lifting or lowering the tone arm.
5.3.4.4 Another angle to be adjusted is the tangential tracking angle (TTA). With tangential tone arms it
must be insured that the system is mounted to lead the stylus exactly along the radius of the disc.
With conventional (pivoted) tone arms a compromise must be made by adjusting the position
of the stylus (= effective tone arm length) with the help of gauge, generally supplied by precision
equipment manufacturers.
5.3.4.5 A high quality, low noise preamp capable of reproducing the standard RIAA curve as well as
reproducing a flat transfer of the audio will be required. If pre-1955 records are being transferred,
then a preamp capable of coping with the equalisation variations listed in Table 2 Section 5.3
Equalisation Chart for Pre-1955 LP Records, may be necessary. Multiple setting preamplifiers are
not readily available, and it may be preferable to modify the equalisation after the normal preamp
output, or applying custom equalisation to a flat transfer in the digital domain.
5.3.4.6 Vital to calibrating the replay chain is a test record cut with the recording characteristics of the
records being transferred, and adjusting the frequency band of a graphic or parametric equaliser
to achieve the proper output. An accurate RIAA test disc can be used to calibrate the system
for non RIAA equalisation providing the characteristics of the replay curve are known. Finding an
47
appropriate test record may prove difficult and even if available, older test records can suffer from
wear and no longer give an accurate response, especially at the higher frequencies.
5.3.4.7 The vast range of playback components available in the 1960s and 1970s is no longer offered, and whilst
not as difficult to locate as replay equipment for 78s, a much more limited range is now available.Though
relatively impervious to damage and decay, LPs can become inaccessible if suitable replay equipment
becomes unavailable. Although a good stock of spares and consumables is recommended for medium
term access, it is important to note that styli and assemblies do not have an infinite shelf life.
5.3.5 Speed
5.3.5.1 Adherence by the recording companies to the standards reduced concern regarding speed setting
that was common with earlier formats. A turntable equipped with strobe measurement and manual
adjustment of speed is recommended as a minimum to ensure replay equipment complies with
standards. The use of a crystal oscillator drive is preferable.
5.3.6 Replay Equalisation
5.3.6.1 The need for equalisation and the manner in which it was developed is explained in Section 5.2.6.
Equalisation is also applied to microgroove recordings and primarily involves reducing the level of
frequencies below about 500 Hz which is the LF turnover below which the recording is constant
amplitude, and boosting those above about 2 kHz. Between 500 Hz and 2 kHz the recording is
characterised by constant velocity (see 5.2.6). The application of equalisation in the recording
process has to be compensated for in the replay chain. Many companies had their own, usually
minor, variations on this theme, and for accurate reproduction, exact replay equalisation needs to be
applied (see Table 1 Section 5.3 below).
5.3.6.2 Records made after about 1955 complied with what is now known as the RIAA (Record Industry
Association of America) curve which became a well observed standard throughout the industry.
RIAA replay characteristics are defined by a replay cut of 6 dB/octave from 20 Hz to 500 Hz, a flat
shelf between 500 Hz and 2.12 kHz (318 µs and 75 µs respectively) and a 6 dB/Octave treble cut
from 2.12 kHz. The flat shelf is approximately 19.3 dB below zero.
5.3.6.3 The Equalisation curves for replay are listed below.
Equalisation Curves by
Name
AES
FFRR (1949)
FFRR (1951)
FFRR (1953)
LP/COL
NAB
Orthophonic (RCA)
629
RIAA
LF Roll-off
50 Hz
40 Hz
100 Hz
100 Hz
50 Hz
50 Hz
LF Turnover
400 Hz (375)
250 Hz
300 Hz (250)
450 Hz (500)
500 Hz3
500 Hz
500 Hz
629 Hz (750)
500 Hz4
Table 1 Section 5.3 Equalisation Curves by Name
3 modified from NAB: less bass below 150 Hz, requiring about 3 dB boost.
4 RIAA and NAB are very similar.
48
(-6 dB/octave, except
where marked)
2500 Hz
3000 Hz*
2120 Hz
3180 Hz (5200)
1590 Hz
1590 Hz
3180 Hz (5200)
Roll-off @
10 kHz
-12 dB
-5 dB
-14 dB
-11 dB (-8.5)
-16 dB
-16 dB
-11 dB (-8.5)
2500 Hz
-13.7 dB
Equalisation Chart for
Pre-1955 LP Records5
Audio Fidelity
Capitol
Capitol-Cetra
Columbia
Decca
Decca (until 11/55)
Decca FFRR (1951) 3dB slope
Decca FFRR (1953) 3dB slope
Ducretet-Thomson
EMS
Epic (until 1954)
Esoteric
Folkways
HMV
London (up to LL-846)
London International
Mercury (until 10/54)
MGM
RCA Victor (until 8/52)
Vox (until 1954)
Westminster (pre-1956)
or
LF Roll-off
100 Hz
100 Hz
100 Hz
50 Hz
LF Turnover
500 Hz (NAB)
400 Hz (AES)
400 Hz (AES)
500 Hz (COL)
400 Hz (AES)
500 Hz (COL)
300 Hz (250)
450 Hz (500)
450 Hz (500)
375 Hz
500 Hz (COL)
400 Hz (AES)
500 Hz (COL)
500 Hz (COL)
450 Hz (500)
450 Hz (500)
400 Hz (AES)
500 Hz (NAB)
500 Hz (NAB)
500 Hz (COL)
500 Hz (NAB)
400 Hz (AES)
(-6 dB/octave, except
where marked
1590 Hz
2500 Hz
2500 Hz
1590 Hz
2500
1590 Hz (1600)
2120 Hz
2800 Hz
2800 Hz
2500 Hz
1590 Hz
2500 Hz
1590 Hz
1590 Hz
2800 Hz
2800 Hz
2800 Hz
2800 Hz
2120 Hz
1590 Hz
1590 Hz
2800 Hz
Roll-off @
10 kHz
-16 dB
-12 dB
-12 dB
-16 dB
-12 dB
-16 dB
-14 dB
-11 dB(-8.5)
-11 dB(-8.5)
-12 dB
-16 dB
-12 dB
-16 dB
-16 dB
-11 dB(-8.5)
-11 dB(-8.5)
-11 dB
-11 dB
-12 dB
-16 dB
-16 dB
-11 dB
Table 2 Section 5.3 Equalisation Chart for Pre-1955 LP Records
5
This information is taken from several sources: the “Dial Your Discs” chart which appeared in High Fidelity magazine during the early
1950s, the chart compiled by James R. Powell, Jr. and published in the ARSC Journal, and the jackets of various early LPs. “Turnover”
(col. 2) is the frequency below which the record manufacturer diminished the bass when mastering the disc, requiring a corresponding
boost during playback. In the chart, turnover is stated using the name of the recording curve, as given on most older pre-amps; a list of
these curves and their turnover frequencies is at the end of the chart. “Roll-off ” (col. 3) is the amount of treble cut at 10kHz required
during playback to compensate for pre-emphasis added during disc mastering. In the chart, roll-off is stated in dB.
49
5.4 Reproduction of Analogue Magnetic Tapes
5.4.1 Introduction
5.4.1.1 Analogue magnetic tape recording technology has permeated every area of the recording industry
since its mass distribution and popularisation in the post WWII era. Technological advancements
made tape the primary recording format for professional recording studios, and manufacturing
developments made the reel recorder affordable for the domestic market. The introduction of the
Philips Compact Cassette in 1963 put a recording device within the grasp of many people and it
became possible and practical for people to record whatever seemed important to them. Virtually
every sound archive and library holds analogue magnetic tape recordings, and PRESTO (Wright and
Williams 2001) estimates there are over 100 million hours of analogue tape recordings in collections
throughout the world, a figure in no way contradicted by the IASA survey of endangered carriers
(Boston 2003). Since the 1970s sound archivists recommended quarter inch analogue reel tape as
the preferred archival carrier, and in spite of inherent noise and impending chemical decay, some
still stand by them today as a stable carrier. Nonetheless, the imminent demise of the analogue tape
industry and the consequent and almost total cessation of the production the replay equipment
demand that immediate steps be taken to transfer this vast store of recorded cultural history to a
more viable system of management.
5.4.1.2 Magnetic tape was first made commercially available in Germany in 1935, but it was the
commercialisation of the American market after 1947 that drove its popularity and eventual
standardisation. The first tapes were manufactured on a cellulose acetate backing and this continued
until the introduction of polyester (polyethylene terephthalate PET, commercially known as Mylar).
Tape manufacturers produced both acetate and PET tapes with an acetate binder, which was
gradually, and most commonly, replaced from the late 1960s by a polyester urethane binder. BASF
manufactured tapes on PVC from the mid 1940s until 1972, though it gradually introduced its own
range of polyester from the late 1950s onward. Though PVC was primarily the province of the
German manufacturer BASF, 3M also produced a PVC tape from around 1960; Scotch 311. Rarer
are paper backed magnetic tapes, which date from the late 1940s to the early 1950s. Cassette
tapes have always been manufactured on polyester. In 1939 the magnetic pigment used was γ Fe2O3,
often called the oxide, and although subsequent improvements in particulate size, shape and doping
increased performance and reduced noise, this formulation has remained virtually the same for
almost all analogue reels and type I cassettes. Type II cassettes are CrO2 or cobalt doped Fe3O4, III
(rarely encountered) are dual layered with both γ Fe2O3 and CrO2 and IV are metal (pure iron).
5.4.1.3 The materials that bind the magnetic particles to the tape substrate, called binders, are often
identified as that part of the tape most susceptible to chemical breakdown. This is especially so with
polyester urethane binder tapes which most commonly use a PET substrate from the 1970s, though
AGFA and BASF and their subsequent owners, Emtec, used a PVC based binder on many of their
studio and broadcast tapes, notably 468.
5.4.2.1 Recordable media such as magnetic tape tend not to have multiple copies of the same generation.
With the exception of cassette, audio on tape was only infrequently mass replicated and so the
sound archivist must choose between generational duplicates. As a rule, the most original copy is the
best copy to select for the purposes of preservation. However, the original tape may have suffered
some form of physical or chemical degradation, such as hydrolysis, whereby a duplicate made in
accordance with proper procedure prior to that decay might be better. Tape rarely shows visible
50
signs of decay or damage so, where multiple copies of an item exist, the best approach is to carefully
spool through, and then audition the tape to determine the best copy.
5.4.2.2 Curatorial decisions must also be made to ensure that the most appropriate or complete duplicate
is selected. This is primarily an issue where the tapes have been produced as a result of a sequential
production process such as audio mastering or in the production of sound for film or video.
5.4.3.1 Tape Cleaning: Dirty or contaminated tapes should be cleaned of dust and debris with a soft brush
and low vacuum before spooling. Deformed reels may seriously damage tapes, especially in the
fast winding mode, and must be replaced before any further steps are carried out. The tape should
be carefully spooled guiding the tape so as not to cause damage. The tape may then, if necessary,
be spooled on a tape-cleaning machine that has a soft cloth or other lint free material cleaning
surface. This may also be beneficial after treatment for hydrolysis (see below). Some tape cleaning or
restoration machines pass the tape across a sharp surface or blade, which removed the top layer of
oxide. Such machines were developed for the re-use of recorded tapes and are not recommended
for archival tapes. Special attention should be paid to dirty cassette tapes as some reputable double
capstan machines may damage dirty tapes during replay. Without adequate tape tension control a
loop may develop between the capstans.
5.4.3.2 Leader Tapes and Tape Splices: Many tapes have splices either through editing or the addition leader
tapes. Such splices are likely to have failed, either through dry failure of the adhesive, or bleeding of
the adhesive layer. The former must be replaced. Bleeding splices constitute a more serious problem.
The adhesive may spread from the splice to the adjacent layers which may have encouraged the
dissolution of the binder. It may also cause the layers to adhere to each other and increase speed
fluctuations. Old adhesive must be removed using a solvent that does not damage the binder. Highly
purified light fuel is an appropriate solvent and may be applied using a Q-tip or lint free cloth. It
is advisable to keep the amount applied to the tape to the minimum required, and no more than
would be applied with a Q-tip. As with all solvents, a small amount should be tested on an unused
portion of the tape. The tape should be left unwound for a few minutes to ensure full evaporation.
Evaporation may be accelerated by an air stream. It is sometimes necessary to replace or add leader
tape to enable the complete recording on the tape to be played.
5.4.3.3 Hydrolysis (Sticky Shed Syndrome): When replayed, many of the tapes manufactured since the
1970s show the artefacts of a chemical breakdown of the binder. Often described as sticky shed
syndrome, the main component of the reaction is hydrolysis1, by which term it is often described.
It is typified by a sticky brown or milky deposit on tape heads and fixed guides, often accompanied
by an audible squeal and reduction in audio quality.
5.4.3.4 The following treatments represent various approaches to the treatment of binder degradation:
5.4.3.4.1Room Temperature, Low Humidity: Hydrolysis involves the splitting of a chemical bond
through the introduction of water, and providing that an irreversible recombination has not
subsequently occurred, hydrolytic reactions should be reversible through the simple process
of removing all water. This can be achieved by placing the tapes in a chamber approaching
0% relative humidity (RH) for extended periods of time, up to several weeks. Slightly
elevating the temperature increases the reaction time. Tests have shown that this treatment,
while successful in some cases does not always completely reverse all the artefacts of a
degraded tape (Bradley 1995).
1
Hydrolysis: A chemical decomposition by addition of water, or a chemical reaction in which water reacts with a compound to
produce other compounds.
51
5.4.3.4.2Heated Respooling: Sometimes very degraded tapes may bind one layer upon another and
uncontrolled spooling may cause damage. In such cases, if baking is not being undertaken,
it may be possible to apply warm dry air directly to the point in the tape pack where the
tape is sticking, and then commence to unspool the tape at a controlled rate of 10–50 mm
per minute.
5.4.3.4.3 Elevated Temperature, Low Humidity: An approach commonly used in the treatment of
hydrolysed tapes is heating the tape in a chamber at a stable temperature approaching
50ºC and 0% RH for period of around 8–12 hours. The temperature of 50ºC probably
equals or exceeds the glass transition temperature2 of the tape binder, however, whether
that has a long term effect on the physical characteristics of the tape when returned to
room temperature is unclear. It does, however, have a positive short term electro-acoustic
effect by returning the replay characteristics to original condition. Interleaving with new
tape may be of benefit in reducing the level of print activity, which can be activated by
temperature increases. Tapes should be rewound a number of times to reduce the effects
of print through caused by elevated temperatures (see 5.4.13.3).
5.4.3.4.4 This latter procedure has a high success rate, but should not be carried out in a domestic
oven. Domestic ovens have poor temperature control, which may exceed safe thresholds.
Additionally the thermostat control of such ovens cycles back and forward across of range
of temperatures and this action may damage the tape. A microwave oven should never
be used as it heats small parts of the tape to very high temperature and may damage the
tape and its magnetic characteristics. A laboratory oven is preferred, or other stable low
temperature device. Higher temperatures should never be allowed as these may cause
deformation of the tape.
5.4.4.5 Exposing tapes to controlled, elevated temperatures as described above should be undertaken very
carefully and only where absolutely necessary.
5.4.4.6 Restoration may be only temporary, yet should enable replay for transfer. Anecdotal evidence is that
hydrolysed tapes which require longer treatment are becoming more prevalent.
5.4.4 Replay equipment: Professional Reel Machines
5.4.4.1 As analogue reel tape has been the mainstay of the sound recording and archiving community for
decades the virtual cessation of the manufacture of reel player/recorders is a major crisis in the
sound archiving community. Very few new professional tape machines are currently available from
manufacturers, possibly only from Otari who continue to make a single machine, which may be
described as the third generation of their mid-range model when compared to their earlier range,
and Nagra Kudelski, who still list two portable field recording analogue tape machines as available.
Not all machines meet the necessary replay specification (below) and archives must check for
compliance before making a purchase. The alternative is to purchase and restore second hand
machines, and the market in high end analogue reel machines is quite strong. It is recommended
that only widely used machines should be purchased as this will facilitate the acquisition of parts and
maintenance. The characteristics of a suitable archival reel machine include the following:
2
Glass Transition Temperature; That temperature at which an adhesive loses its flexibility and becomes hard, inflexible, and “glasslike.”
52
5.4.4.2 Reel Replay Speeds: The standard tape speeds are as follows: 30 ips (76.2 cm/s), 15ips (38.1 cm/s),
7½ ips (19.05 cm/s), 3¾ ips (9.525 cm/s), 17/8 ips (4.76 cm/s) and 15/16 ips (2.38 cm/s). The need to
replay all these speeds will depend on the makeup of the individual collections. No single machine
will play all 6 speeds, but it is possible to cover all speeds with two machines.
5.4.4.3 Mono and stereo ¼ inch recording equipment come in 3 basic track configurations; full track, ½
track and ¼ track. There are variations in the actual track width according to the particular standard.
A tape replayed with a head with less replay width than the actual recorded track width will exhibit
an altered low frequency response known as the fringe effect, and show poorer signal to noise than
optimum. So a recorded track width of 2.775mm replayed with a 2mm stereo head will result in a
loss of signal to noise ratio of approximately 2dB. The fringe effect is of the order of about +1dB
at 63 Hz at 19.05 cm/s (7½ ips) (McKnight 2001). A tape replayed with a head with a wider replay
width than the actual recorded track width will exhibit slightly worse signal to noise and may pick
up unwanted hiss or signal from adjacent tracks. “It amounts to the ratio of 1.9 mm to 2.1 mm,
corresponding to a 1 dB level shift for these head widths; or 1.9 mm to 2.8 mm, corresponding
to 3.3 dB for these widths.” (McKnight 2001) In practice these compromises are often accepted
for small variation in track width in replay provided no unwanted signal is included (note that
the unrecorded portion of previously erased tape may exhibit higher noise levels). Though some
machines may include ½ track and ¼ track replay heads, it may be necessary to have more than
one machine to deal with these standards.
B
A
A
B
IEC1 94-1
(pre 1985)
6.3 mm,
(0.248 in)
6.3 mm,
(0.248 in)
NAB 1965
6.3 mm,
(0.248 in)
6.05 mm
(0.238 in)
IEC 94-6
1985
6.3 mm
(0.248 in)
5.9 mm
(0.232 in)
Fig 1, section 5.4 full track head configuration and dimensions.
53
B
C
A
Ampex
IEC 94-6
1985 2 track
IEC home stereo (pre
1985)
NAB 1965
IEC-1 Time code
DIN mono half track
IEC 94-6
1985 Stereo
IEC-1 Stereo (pre 1985)
Mono half track
IEC
½ inch
6.3 mm,
(0.248 in)
6.3 mm,
(0.248 in)
6.3 mm,
(0.248 in)
6.3 mm,
(0.248 in)
6.3 mm,
(0.248 in)
6.3 mm,
(0.248 in)
6.3 mm,
(0.248 in)
12.6 mm
(0.496 in)
maximum
recording
width3
6.05 mm
(0.238 in)
5.9 mm
(0.232 in)
6.3 mm,
(0.248 in)
6.05 mm
(0.238 in)
6.3 mm,
(0.248 in)
5.9 mm
(0.232 in)
6.3 mm,
(0.248 in)
B
1.9 mm
(0.075 in)
1.95 mm
(0.077 in)
2.0 mm
(0.079 in)
2.1 mm
(0.082 in)
2.3 mm
(0.091 in)
2.58 mm
(0.102 in)
2.775 mm
(0.108 in)
5.0 mm
(0.197 in)
A
C
2.14 mm
(0.084 in)
2.00 mm
(0.079 in)
2.25 mm
(0.089 in)
1.85 mm
(0.073 in)
1.65 mm
(0.065 in)
0.75 mm
(0.03 in)
0.75 mm
(0.03 in)
2.5 mm
(0.098 in)
Fig 2, section 5.4 two track and half track head configuration and dimensions.
B
IEC1
NAB
C
A
A
B
6.3 mm,
1 mm
(0.248 in) (0.043 in)
C
0.75 mm
(0.43 in)
C
B
C
Fig 3 section 5.4 quarter track head configuration and dimensions.
3 Maximum recording width refers to the width measured from the outside edge of the outer tracks (see section 5.4.4.4)
54
IEC
Philips
A
B
C
3.81 mm, 0.6 mm, 0.3 mm
(0.15 in) (0.02 in). (0.012 in)
A
B
C
B
Fig 4 Section 5.4 Stereo Cassette head configuration and dimensions.
ANSI
Philips
A
A
3.81 mm,
(0.15 in)
B
1.5 mm,
(0.06 in)
B
Fig 5 Section 5.4 Mono Cassette head configuration and dimensions.
5.4.4.4 Head dimensions are specified in different ways in the European and US standards. Initially,
the International Electrotechnical Commission (IEC), predominately referred to by European
manufacturers, specified the tape with regard to the centre of the tape and the distance between
the tracks, while the American based standards referred to the size of the recording track width
defined diagrammatically with respect to one side. The size of the tape itself, has changed over
time, initially a quarter of an inch, it was defined as 0.246 ± 0.002 inch (6.25 ± 0.05 mm) and later
as 0.248 ± 0.002 in (6.3 ± 0.05 mm)”. IEC defines recording width in a full track recording in the
following manner, “A single track shall extend over the whole width of the tape.” (IEC 94 1968:11),
whereas the American based standards define the size of the recorded track to slightly less than
the width of a 0.246 inch tape at 0.238 +0.010 -0.004 inch track size (this is a pragmatic solution to
the problem of “grooves” in head wear and extends to all track dimensions). IEC later changed their
full track width to 5.9 mm (0.232 inches). The number of standard track widths specified in figs.1 to
5 suggests that there is very little standardisation. (Eargle 1995, Benson 1988, IEC 94-1 1968, 1981,
IEC 94-6 1985, NAB 1965 McKnight 2001, Hess 2001).
5.4.4.5 The net effect of replaying tapes on mismatched head widths is discussed in 5.4.2.2 above. It
is important to attempt to assess the correct head width with which the original tapes were
recorded and to then replay them on the most appropriate machine available. ½” and 1” two
track recordings are generally made in ½ track configuration only, and with specialised professional
recording equipment with the intention of providing very high quality analogue audio. The same type
and standard of equipment is required for replay, and an even closer attention to the detail of the
record/replay standards.
55
5.4.4.6 Multitrack recordings range from domestic ¼” standards to professional 2” and care must be
taken to ensure the replay of those tapes is accurate. If time code has been recorded as part
of the recording it must be captured and encoded in such a way that it may be used for later
synchronisation (see 2.8 for file formats).
5.4.4.7 Tape machines should be capable of replaying signals with a frequency response of 30 Hz to 10 kHz
±1 dB, and 10 kHz to 20 kHz +1, -2 dB.
5.4.4.8 The equalisation on a reel replay machine should be capable of being aligned for replaying NAB or
IEC equalisation, preferably being able to switch between them without re-alignment.
5.4.4.9 Wow and flutter unweighted better than 0.05% at 15 ips, 0.08% at 7½ ips, and average variation
from true speed better than 0.1%.
5.4.4.10 A professional archival reel machine should also have gentle tape handling characteristics so
that it does not damage the tape during replay. Many of the early and middle generation studio
machines depended on the robust characteristics of the modern tape carrier for their successful
operation. These machines may cause damage to older tapes, or to long play tapes or thin tapes
used for field recording.
5.4.5 Replay equipment: Professional Cassette Machines
5.4.5.1 Professional cassette replay machines are unavailable new. Also, the second hand market for
professional cassette machines is not as strong as that for reel machines making it difficult to locate
appropriate equipment. This represents a critical problem for sound archives, many of whose
collections hold large numbers of recorded cassette tapes. Thus it should be a matter of priority for
any collection with cassette tapes to seek out and acquire professional cassette replay machines.
The characteristics that distinguish a professional machine from a domestic machine, apart from the
replay specification, include solid mechanical construction, the ability to adjust replay characteristics
and head azimuth, and the provision of balanced audio outputs. Many high quality audiophile
machines provide some of the above characteristics. The characteristics of a suitable archival cassette
replay machine include the following:
5.4.5.2 Replay speeds 17/8 ips (4.76 cm/s) (note that speeds of 15/16 ips and 3 ¾ ips may also be required
for replay of specially recorded cassettes).
5.4.5.3 Variation from speed better than 0.3%. Wow and flutter weighted better than 0.1%.
5.4.5.4 Replay frequency response of 30 Hz to 20 kHz +2, -3 dB.
5.4.5.5 Ability to replay Type I, II, and IV cassettes (as required).
5.4.5.6 Most cassette machines will automatically select the correct replay equalisation by reading the holes
or notches on the top of the cassette housing or shell to determine the tape type. A few machines
do not read the notches but have a switch that the operator uses to select the appropriate
equalisation. Type III cassettes may be problematic as they are enclosed in shells identical to Type I
cassettes, while requiring the same replay equalisation curve as Type II cassettes. Where no explicit
option to replay Type III has been provided by the playback machine, it may be necessary to use
a deck with adjustable equalisation or to rehouse the tape in a Type II shell (see Section 5.4.12.5
Cassette Enclosures).
56
5.4.6 Maintenance
5.4.6.1 All equipment will require regular maintenance to keep it in working order. However, as analogue
replay equipment is going out of production, it is necessary to make plans for spare parts as
manufacturers will only maintain spare parts for a finite, and possibly short, period of time.
5.4.7 Alignment (equalisation below)
5.4.7.1 Analogue equipment requires regular alignment to ensure that it continues to operate within
specification. It is recommended that heads and tape path be thoroughly cleaned every 4 hours of
operation, or more frequently if required, using a suitable cleaning fluid such as isopropyl alcohol on
all metal parts. Rubber pinch rollers should be cleaned with dry cotton buds or with cotton buds
dampened with water as necessary. The older, original rubber pinch rollers can gradually become
brittle if cleaned with alcohol, increasing wow and flutter. The new generation of polyurethane pinch
rollers, generally coloured dark green, may dissolve if cleaned with alcohol. Heads and tape path to be
demagnetised every 8 hours of operation, tape path and replay characteristics checked for alignment
every 30 hours of use and equipment should receive a total alignment and check every 6 months.
5.4.7.2 In the same way that machines and tape are going out of production, suitable test tapes are likewise
becoming difficult to obtain, and some are now unobtainable. It behoves the archivist to acquire
enough open reel and cassette test tapes to manage the transfer of their collection.
5.4.8 Speed
5.4.8.1 Although speed correction is also possible in the digital domain, it is better to avoid such later digital
correction and to carefully choose replay speed in the first transfer process, and to document
chosen speed and justification. Tape recorders are very likely to have exhibited inaccurate speed
characteristics due to fault, poor alignment, or in some cases, unstable power supply. Consequently
no tape speed should be taken for granted.
5.4.9 Capstan-less Machines and Non-Linear Speeds
5.4.9.1 Some early generation reel recording machines were designed to run without the control of the
capstan and pinch roller, and consequently exhibit steadily increasing speed. If these tapes are played
at a standard, unchanging speed, the resultant signal would decrease in pitch as the tape was replayed.
To play the tape correctly the replay speed must change in the same manner as the recording speed.
Some of the more recent replay machines, such as those made by Nagra or Lyrec, have incorporated a
voltage driven external speed control which allows the operator to design a simple circuit with a curve
that matches the speed of the original. Some of the last generation replay machines, such as the Studer
A800 series, incorporated microprocessor control allowing for programmable manipulation of the
speed, and others like the Lyrec Frida allowed the speed to be manipulated in the MIDI environment.
However, care should be taken in assuming that the speed increase is linear. The early capstan-less
machines were made cheaply and the speed varied according to the load on the reel, the speed
increase is often less at the beginning or end of the tape where one or the other of the reels is full
making a graph of the replay speed over time far from linear.
5.4.10 Replay Equalisation
5.4.10.1The signal representation in most analogue audio formats is deliberately not linear in terms
of frequency response. Correct replay, therefore, requires appropriate equalisation of the
frequency response.
57
5.4.10.2The most common of the equalisation standards for audio replay of analogue tape are as set out
below (Table 1 Section 5.4). It should be noted that equalisations have developed over time. The
current standards are given in bold type, together with their date of introduction. Earlier recordings
must be replayed by applying the respective historical standards and simple additional circuits may
be utilised. The overlapping of old and new standards should be taken into account when decisions
are to be made for tapes recorded in times of transition. Prior to that there were a number of
manufacturers’ standards.
30 ips, 76 cm/s
30 ips, 76 cm/s
15 ips. 38 cm/s
15 ips. 38 cm/s
7½ ips, 19 cm/s
7½ ips, 19 cm/s
7½ ips, 19 cm/s
7½ ips, 19 cm/s
3¾ ips 9.5 cm/s
3¾ ips 9.5 cm/s
3¾ ips 9.5 cm/s
3¾ ips 9.5 cm/s
3¾ ips 9.5 cm/s
3¾ ips 9.5 cm/s
17/8 ips 4.75 cm/s
IEC2
AES
CCIR
IEC1
DIN
IEC1
CCIR
DIN
BS
NAB
EIA
IEC1
DIN(studio)
CCIR
IEC 2
NAB
DIN(home)
EIA
RIAA
Ampex (home)
EIA (proposed)
CCIR
IEC
DIN
BS
IEC2
NAB
RIAA
DIN
DIN
(1981) current standard
∞
17.5 μs
(1953–1966)
(1968)
(1962)
(1953)
(1962)
∞
35 μs
∞
35 μs
1963
1965
1966
(1965) current Standard
(1966)
(1963)
(1968)
3180 μs
50 μs
∞
70 μs
3180 μs
50 μs
(1967)
∞
50 μs
(up to 1966)
(up to 1968)
(up to 1965)
∞
100 μs
(1965)
(1968)
(1962)
(1955–1961)
3180 μs
90 μs
3180 μs
∞
120 μs
200 μs
Ampex (home)
EIA (proposed)
IEC
Ampex
IEC
DIN
(1967)
∞
100 μs
(1962–1968)
(1953–1958)
(1971)
3180 μs
3180 μs
3180 μs
140 μs
200 μs
120 μs
58
17/8 ips 4.75 cm/s
IEC
DIN
RIAA
IEC Type I
(1968–1971)
(1966–1971)
(1968)
1974 current standard
1590 μs
120 μs
3180 μs
120 μs
17/8 ips 4.75 cm/s
cassette
17/8 ips 4.75 cm/s
cassette
DIN Type I
(1968–1974)
1590 μs
120 μs
Type II and IV
(1970) Current standard
3180 μs
70 μs
/ ips 2.38 cm/s
undefined
17/8 ips 4.75 cm/s
cassette
15 16
Table 1 Section 5.4 Common Equalisation Standards for Audio Replay of Analogue Tape4
5.4.10.3At 15 ips and 7½ ips there is a choice in replay equalisation for reel tapes even for tapes which
were recently recorded according to the current standards. However, these are the two most
common recording speeds, and care must be taken when choosing a replay equalisation to ensure
that it corresponds with the record equalisation. Apart from the standards mentioned in table
1 section 5.4 there are a small number of more current standards intended to achieve better
performance but which are different from the commonly accepted standards. At 15 ips Nagra
tape recorders have the option to use a special equalisation called NagraMaster. The US version
of NagraMaster had time constants 3150 and 13.5 μs, the European version of NagraMaster had
time constants ∞ and 13μs. Ampex used “Ampex Master Equalization” (AME), also at 15 ips but
officially only on particular ½ inch mastering recorders introduced in 1958 and sold for several
years following (MRL 2001). Logging machines and some popular semi-professional portable
equipment were able to record at the very slow speed of 15/16 ips (2.38 cm/s). However, it appears
that there is no agreed exchange standard for these tapes and any equalisation would have adhered
to proprietary conventions.
5.4.10.4Sometimes any lack of documentation may require the operator to make replay equalisation
decisions aurally. Cassette replay equalisation corresponds to the tape type, and care must be taken
to ensure that the correct replay equalisation is used. Many tape recordings, specifically private
recordings and those of cultural or research institutions that lacked technical support, have been
made on un-aligned tape recorders. Unless there is objective evidence that would allow alternate
settings, with regard to equalisation, tapes must be treated as properly aligned.
5.4.11 Noise Reduction
5.4.11.1The signal recorded onto a tape may have been encoded in such a way as to mask the inherent
noise of the carrier. This is known as noise reduction. If the tape has been encoded while recording,
it must be decoded using the same type of decoder appropriately aligned. The most common noise
reduction systems include Dolby A, and Dolby SR (professional), Dolby B and Dolby C (domestic),
dbx types I (professional) and II (domestic)although rarely used and TelCom.
4
Note, IEC refers to IEC Pub 60094-1 4th edition, 1981, NAB to the NAB reel to reel standard 1965 (IEC2), or cassette standard
1973, DIN refers to DIN 45 513-3 or 45 513-4 and AES to AES-1971, and BS to the British Standard BS 1568). Thanks to Friedrich
Engel, Richard L. Hess and Jay McKnight for generously supplying information on tape equalisation.
59
5.4.11.2The alignment of the record and replay characteristics of the tape machine are critical to the
adequate operation of noise reduction systems and characteristic line up tones are often included
on professionally recorded tapes. The output level, as well as the frequency response can alter the
response of the decoding system and it is also important to note that noise reduction may be
applied to either IEC or NAB equalisation and must be replayed correctly. Dolby B and Dolby C
have routinely been included in most professional cassette decks of recent years and generally do
not have line up tones and have a less obvious effect on the signal than the professional systems.
5.4.11.3Though it is possible to transfer the audio from an encoded tape for decoding at a later time, the
multiple variables in alignment can compound the errors and make it difficult to decode accurately
once the tape has been transferred. Decoding is better undertaken at the time of transfer.
5.4.11.4Unless documented, it is difficult to assess whether compact cassettes have encoded with a noise
reduction system. As with equalisation, the lack of documentation may require the operator to make
such decisions aurally. The right replay is generally characterised by an even level of background hiss,
while the fluctuation of this level indicates a wrong playback setting. A spectrum analysis tool can be
helpful. If it cannot be determined, copies of cassettes should be made flat.
5.4.12.1Misalignment of recording equipment leads to recording imperfections, which can take manifold
form. While many of them are not, or hardly correctable, some of these faults can objectively be
detected and compensated for. It is imperative to take compensation measures in the replay process
of the original documents incurred, as no such correction will be possible once the signal has been
transferred to another carrier.
5.4.12.2Azimuth and Tape Path Alignment: Inaccurate alignment of the record head of the original
recording machine means that at replay, the signal retrieved will exhibit a reduced high frequency
response, and, in the case of two or more track replay, an altered phase relationship between the
two channels. Adjustment of the angle of the replay head such that the relationship of the head is
in the same plane as the magnetised field on the tape is termed the azimuth adjustment and this
simple adjustment can markedly improve the quality and intelligibility of the retrieved signal. There
is no difficulty in training staff in this task, and good binaural hearing is all the measuring technology
required. An accurate phase meter or oscilloscope will aid in the adjustment of mono and
properly recorded tapes, they may, however, be misleading on tapes recorded on cheap, domestic
equipment. In such cases aural judgement of the high frequencies should be relied on. Additionally
or alternatively, a software programme providing a real time-spectrogram function can be used.
Azimuth adjustment should be a routine part of all magnetic tape transfers.
5.4.12.3Digital systems may correct the phase relationship of the signal (often described as azimuth
correction), however such procedures cannot retrieve the high frequency information that is lost.
Azimuth adjustments must be made on the original tape before transfer commences.
5.4.12.4The vertical alignment of the heads on the original recording machine may present an obstacle
to the appropriate reproduction of the signal. This is particularly the case with recordings made
on amateur or consumer-grade equipment. In order to obtain a visual representation of the
alignment of the tracks on the tape of a recording the following procedure should be followed:
Recorded portions of tapes should be protected by a very thin transparent sheet of Mylar or similar
transparent material. A powder or suspension of ferromagnetic material, particle size less than
3 µm, is sprayed over the transparent sheet. The magnetic properties of the recorded portion of
60
the tape then make the tracks visible. A carefully marked series of measurement lines on the sheet
will aid in detecting misalignment. These tape path adjustments are less frequently required than
azimuth adjustment, but if they must be undertaken the replay equipment should be recalibrated by
a qualified technician. Every care should be taken to ensure no iron particles remain in contact with
the tape as these may damage the replay heads.
5.4.12.5Cassette Enclosures: The enclosures in which low cost cassette tapes are housed may cause the
tape to jam or replay with increased wow and flutter. In such cases it is often beneficial to replace
the tape in a high quality screwed enclosure being sure to include the rollers, pressure pad and
lubricating sheets.
5.4.12.6Wow, Flutter and Periodic Tape Speed Variations: There is little that can be done to effectively
improve periodic variations in the recorded signal. It is therefore imperative that the replay
equipment is thoroughly and carefully checked, aligned and maintained to ensure that no speed
related artefacts are introduced. With the availability of high resolution A/D converters and
components, it seems possible to retrieve the high frequency (HF) bias signal from analogue
magnetic tapes during transfer, which may enable the correction of wow and flutter. There are,
however, many significant barriers to realising this, including a lack of available hardware to extract
signals of such high frequencies and the inherent unreliability of the bias signal itself. As the
procedure is generally time-consuming and complex, and substantial improvements concerning this
matter are not to be expected, implementation is unlikely, and even then, only feasible for a limited
group of tapes produced under specific circumstances.
5.4.13 Removal of Storage Related Signal Artefacts
5.4.13.1It is preferable in most cases to minimise the storage related signal artefacts before undertaking
digitisation. In linear analogue magnetic recording, for example, print-through is a well-known and
disturbing phenomenon. The reduction of this unwanted signal can only be undertaken on the
original tape.
5.4.13.2Print-Through: Print-through is the unintentional transfer of magnetic fields from one layer of
analogue tape to another layer on the tape reel. It reveals itself as the pre and post echoes to
the main signal. The intensity of print through signal is a function of the wavelength, tape coating
thickness, but primarily the spread of the coercivity5 of the particles in the magnetic layer. Almost
all print through occurs soon after the tape is recorded and wound onto the pack. The increase in
print-through after this reduces over time. Further significant increases in print-through occur only
as a consequence of changes in temperature. When the tape is stored with the oxide facing in to
the hub, the most common standard, the print on the layer outside of the intended signal is stronger
then the print signal on the layer towards the hub of the spool. Consequently it has been frequently
recommended that tapes be stored “tail out”, in which case the post echoes are louder than the pre
echoes and less obvious. German broadcast standards specified that tapes be wound with the oxide
out, in which case the reverse applies, and tapes should be stored “head out”.
5.4.13.3Printed signals are reduced by the act of rewinding the tape prior to playing, by a process termed
“magnetostrictive action”. Systematic tests have shown, however, that it is wise to rewind a tape at
least three times to sufficiently diminish print through (Ref Schüller 1980). If the printed signal is very
high and it does not respond adequately to rewinding, some tape machines allow the application of
a low level bias6 signal to the tape during playback. This selectively erases lower coercivity particles
5 Coercivity; A measure of the intensity of the magnetic field needed to reduce the magnetization of a ferromagnetic material to zero
after it has reached saturation.
6 Bias; A high frequency signal mixed with the audio during recording to help reduce tape based noise. Devised by Weber in 1940.
61
and hence reduces print-through, though it may also have an effect of the signal, especially if overapplied, and should only be used as a last resort and then very carefully.
5.4.13.4Though print-through can be reduced on the original tape the same level of restoration is not
achievable afterwards. Once copied to another format the printed signal becomes a permanent part
of the wanted signal.
5.4.13.5 Vinegar Syndrome and Brittle Acetate Tape: Acetate tape becomes brittle with age which may
make it difficult to play a tape without breaking. The brittleness occurs as a result of a process of
chemical degradation which occurs when the molecular bonds of the acetate compound break
down to release acetic acid giving off the characteristic smell of vinegar. Broken acetate tape can be
spliced without any signal loss or deterioration, because, as a result of its brittleness, no elongation
of the tape occurs. Brittle tapes, however, are also subject to a variety of deformations which hinder
the necessary tape-to-head contact for optimal signal retrieval. Though a process of re-plastification
would be advantageous, such processes do not exist as yet. Archivists are warned against the chemical
processes sometimes suggested as these may not only jeopardise the further survival of the tape, but
also contaminate replay equipment and, indirectly, other tapes replayed on such machines. Instead, it is
recommended that such tapes be replayed using a recent machine that permits to lower tape tension.
This will enable an acceptable compromise between care of the fragile tape and the application of
enough tape tension to permit the best possible tape-to-head contact.
5.4.13.6Physical Tape Memory: Poorly stored and spooled polyester and PVC tapes may also suffer from
deformation of the tape. The tape will often retain a memory of that deformation and so make poor
tape to head contact, which reduces the signal quality. Repeated respooling and resting may reduce
some of this effect.
5.4.14 Wire Recordings
5.4.14.1Though the principles of wire recordings were demonstrated at the very end of the 19th century,
and various dictation machine manufacturers produced working models in the 1920s and 1930s
(see 5.4.15 below), it was not until around 1947 that the wire recorder was successfully marketed
to the general public.
5.4.14.2The speed of wire recorders was not standard and varied between manufacturers and even, on
occasion, from model to model. After 1947, however, manufacturers mostly adhered to a standard
speed of 24 ips and a reel size of 2¾ inches. Wire recorders did not have capstans, and so the
speed would change as the take up reels became full. The size of the take up spool was integral
to the correct replay of the wire, and very often related to a particular machine or manufacturer.
The take-up spool is generally a fixed part of the machine. The height of popularity of the wire
recorder was in the years from the mid 1940s till the early 1950s, a period which coincided with
the development and introduction of the technically superior tape recorder and the wire was
soon considered obsolete. Even in its heyday, the wire recorder was primarily used as a domestic
recorder, though some were used for commercial purposes.
5.4.14.3Though the wire fell quickly from favour, wires were available in speciality outlets until the 1960s.
Early reel sizes were large in comparison to the 2¾ inch reels which become the most commonly
used reel. Some wires, mostly early in the history of the wire recorder, were made from plated or
coated carbon steel, and these may now be corroded and difficult to play. Many wires, however, are
in excellent condition being made from Stainless Steel with 18% chromium and 8% nickel, and have
not corroded.
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5.4.14.4The principle of wire recorders is comparatively simple, so that the construction of a replay machine
is possible. However, the complexity associated with successfully spooling and playing the fine wire
without tangles or breakages suggest that the best approach to replay is to use an original machine,
though it is worth noting that some experts have modified tape machines to replay wires. When
using original machines it is recommended that the audio electronics be overhauled to ensure best
performance or, preferably, replaced with audio circuitry using modern components (Morton 1998,
King: n.d.)
5.4.15 Magnetic office dictation formats.
5.4.15.1In the decades following World War II a wide variety of magnetically recorded office dictation
formats appeared. That the needs of the office differ from other audio recording environments
is reflected in their design: reduced size and weight, ease of operation and variable speed were
prioritised, usually at the expense of audio quality. Magnetic dictation systems may be broadly
divided into tape and non-tape-based formats.
5.4.15.2Tape in this context includes various forms of wire (see 5.4.14 above), reel and cassette. Some
formats may be playable using standard equipment (non-standard cassette formats may sometimes
be rehoused and replayed in standard cassette shells for instance) while others may only be played
on dedicated format-specific players. Where a choice is available, a decision needs to be made
between the two approaches. One entails the use of high-specification, relatively easy to maintain
standard equipment, potentially coupled with poor compatibility in tape width, head configuration,
replay speed, equalisation, noise reduction etc. The other offers higher compatibility between carrier
and player, but very likely at the cost of the lower specification and esoteric maintenance needs of
the original format-specific equipment. Tape-based formats can be subdivided into linear and nonlinear speed. The former will present fewer problems if replayed on conventional equipment; the
latter may also be playable in this way, but will require speed adjustment (see 5.4.9).
5.4.15.3Non-tape formats include a bewildering array of discs, belts, rolls and sheets, all featuring
magnetically coated surfaces, recorded onto and replayed using heads similar in principle to
conventional tape heads. Given sufficient expertise, time and money therefore, it may be possible to
build replay devices for some of these formats, incorporating components from more common tape
replay equipment. In many cases however locating an original replay machine might be more feasible,
and it may be possible to contract a specialist equipped to carry out the work.
5.4.16 Time Factor
5.4.16.1The time needed for copying contents of audio material varies greatly, and is highly dependent
on the nature and status of the original carrier. The step of actually playing the carrier is only one
part of the process, which includes respooling, assessment, adjustment and documentation. Even
a well documented, good quality analogue tape of 1 hour’s duration will take, on average, twice
the time of the length of its recording to properly transfer to a digital carrier. In the mid-1990s the
Archivarbeitsgruppe of ARD (Arbeitsgemeinschaft der Rundfunkanstalten Deutschlands) would
regard this as optimistic as they postulated a transfer factor of 3 (1 operator: 3 hours of work for
1 hour of material) for the transfer of typical archival holdings of their radio stations. Tapes that
exhibit any faults, which require repair or restoration, or need documentation or the assessment and
addition of metadata, will take much longer to conserve, transfer and preserve.
63
5.4.17 Signal Auto detection, auto upload (failings and benefits)
5.4.17.1It is recommended that all tapes be actively listened to while preservation transfers are being
undertaken. However, in response to the sheer quantity of the material to be transferred and
preserved, manufacturers of digital archiving systems have been developing ways of automatically
monitoring and detecting signal faults allowing for the possibility of unattended transfers. The savings
in time are obvious, as an individual operator may undertake multiple transfers simultaneously.
The systems themselves seem to achieve their greatest benefit on largely homogenous collection
material that is well recorded on stable carriers that can be treated identically. This is evident in
that the most successful mass upload systems have been undertaken or implemented by broadcast
archives where the content is largely of similar quality, the collection size is large, and the resources
are available to build, manage and run such systems. For material that requires individual treatment,
and this is typified in most research and heritage collections, the benefits of an automated system
are not as great.
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5.5 Reproduction of Digital Magnetic Carriers
5.5.1 Introduction
5.5.1.1 Under optimum conditions digital tapes can produce an unaltered copy of the recorded signal,
however any uncorrected errors in the replay process will be permanently recorded in the new
copy or sometimes, unnecessary interpolations will be incorporated into the archived data, neither
of which is desirable. Optimisation of the transfer process will ensure that the data transferred most
closely equates to the information on the original carrier. As a general principle, the originals should
always be kept for possible future re-consultation however, for two simple practical reasons any
transfer should extract the optimal signal from the best source copy. Firstly, the original carrier may
deteriorate, and future replay may not achieve the same quality, or may in fact become impossible,
and secondly, signal extraction is such a time consuming effort that financial considerations call for an
optimisation at the first attempt.
5.5.1.2 Magnetic tape carriers of digital information have been used in the data industry since the 1960s,
however, their use as an audio carrier did not become common until the early 1980s. Systems
reliant on encoding audio data and recording onto video tapes were first used for two track
recording or as master tapes in the production of Compact Discs (CD). Many of these carriers are
old in technical terms and in critical need of being transferred to more stable storage systems.
5.5.1.3 A crucial recommendation of all transfers of digital audio data is to carry out the entire process in
the digital domain without recourse to conversion to analogue. This is relatively straightforward with
later technologies which incorporate standardised interfaces for exchanging audio data, such as AES/
EBU or S/PDIF standards. Earlier technologies may require modification to achieve this ideal.
5.5.2.1 Unlike copying analogue sound recordings, which results in inevitable loss of quality due to generational
loss, different copying processes for digital recordings can have results ranging from degraded copies
due to re-sampling or standards conversion, to identical “clones” which can be considered even better
(due to error correction) than the original. In choosing the best source copy, consideration must be
given to audio standards such as sampling and quantisation rate and other specifications including any
embedded metadata. Also, data quality of stored copies may have degraded over time and may have
to be confirmed by objective measurements. As a general rule a source copy should be chosen which
results in successful replay without errors, or with the least errors possible.
5.5.2.2 Unique Recordings: Original source materials such as multi-track sessions, field recordings, logging
tapes, home recordings, sound for film or video, or master tapes, may include unique content in
whole or in part. Un-edited material may be less or more useful than the edited final product,
depending on the purpose of the archived material. Curatorial decisions must be made to ensure
that the most appropriate or complete duplicate is selected. Truly unique recordings do not present
any choice to the archivist. In the case where content is uniquely held on a single copy within
a collection it is worth considering whether alternative copies might exist elsewhere. It may be
possible to save both time and trouble if other copies exist which are in better condition, or on a
more convenient format.
5.5.2.3 Recordings with Multiple Copies: Preservation principles indicate that copies of digital tape should
ideally be a perfect record of the media content and any associated metadata as recorded on the
original digital document. Any digital copy meeting this standard is a valid source for migration of the
essence to new digital preservation systems.
65
5.5.2.4 In reality, effects of standards conversion, re-sampling or error concealment or interpolation1 may result
in data loss or distortion in copies, and deterioration over time degrades the quality of original recordings
and subsequent copies. As a result, copying outcomes may differ depending on the choice of source
material. Cost can also vary depending on the physical format or condition of the source material.
5.5.2.5 Determining the best source copy requires consideration of recording standards used to create
copies, quality of equipment and processes used, and the current physical condition and data quality
of available copies. Ideally this information is documented and readily available. If this is not so then
decisions must be based on understanding of the purpose and history of various copies.
5.5.2.6 Duplicates on Similar Media: Best source material in this case will be that copy with the best data
quality. First choice will usually be the most recently made unaltered digital copy. Earlier generations
of unaltered digital copies may represent an alternative if the newer copies are inadequate due to
deterioration or improper copying.
5.5.2.7 Copies Differing in Media or Standard: Production or preservation processes may result in
availability of multiple copies on differing digital tape formats. The best source material should be
identical to the original in standard, have the best available data quality, and be recorded on the most
convenient format for reproduction. Judgment is called for if any of these conditions cannot be met.
5.5.2.8 If the digital recordings are only duplicates of analogue recordings, and where the analogue originals
still exist, re-digitisation is an option to consider if those digital copies are inferior in standard, quality
or condition.
5.5.3 Cleaning, Carrier Restoration
5.5.3.1 Magnetic digital tapes are similar in materials and construction to other magnetic tapes, and suffer
from similar physical and chemical problems. Digital tapes achieve high data densities through
the use of thin tapes, small magnetic tracks and ongoing reductions in the size of the magnetised
domains which can be written and read. Consequently even minor damage or contamination can
have major impacts on signal retrievability. All tape degradation, damage or contamination will appear
as increased errors. Carrier restoration problems and techniques are similar for all magnetic tapes,
but since base, binder and magnetic materials are subject to ongoing development any restoration
processes must be tested and proven for specific media.
5.5.3.2 Commercial cleaning machines are available for open reel magnetic tapes and for most videotape
formats commonly used to carry digital audio signals and are effective for moderately degraded
or contaminated tapes. Vacuum or hand cleaning may be indicated for tapes with higher levels of
contamination or of greater fragility, but requires conservatorial care to avoid damaging delicate
tapes and intricate cassette mechanisms. Any cleaning process has potential to cause damage and
should be applied with appropriate caution.
5.5.3.3 Jigs can aid in manipulating tapes and cassette housings, and are commercially available for some
formats. Purpose-built jigs for other formats can be manufactured in a moderately well equipped
mechanical workshop.
5.5.3.4 Digital tapes with polyester urethane binders have the potential to suffer from hydrolysis in the
same way as analogue magnetic tapes. Any rejuvenation of digital magnetic tape will require
tight process control, and should only be attempted in a purpose-built environmental chamber
or vacuum oven2 (see Section 5.4.3 Cleaning and Carrier Restoration). This may be even more
1 Error concealment or interpolation is an estimation of the original signal when data corruption prevents accurate re-construction
of the signal.
2 Vacuum ovens reduce the air pressure in the oven chamber and so better control moisture content.
66
critical with digital recordings as they will often have been made on thinner based tapes housed in
complex cassette mechanisms.
5.5.3.5 Deterioration of magnetic tapes can be minimised by appropriate storage conditions. Standards
for long-term digital magnetic tape storage are generally more stringent than for analogue tapes,
due to their greater fragility and susceptibility to data loss through relatively minor damage or
contamination. Higher than recommended temperature or humidity will promote chemical
deterioration. Cycling of temperature and humidity will result in expansion and contraction of the
tape and may damage the tape base. Dust or other contaminants can find its way onto the tape
surface resulting in data loss and possibly physical damage during replay.
5.5.3.6 After cleaning and/or repairing measures or prior to the reproduction it may be advisable to first
measure the magnetic digital tape’s error rates. The organisation of the data and the type of error
correction used varies according to the tape format. For DAT for example, the error correction
process uses two Reed–Solomon codes arranged in a cross code system, C2 horizontally and C1
vertically. Also, each block of data has a value assigned, known as a parity byte. Counting the Block
parity errors are known as CRC errors, or sometimes as the block error rate. The sub code of the
DAT (Digital Audio Tape) is also subject to errors. Error measurement should include, as a minimum:
5.5.3.6.1 C2 and C1 errors.
5.5.3.6.2 CRC or Block error rate.
5.5.3.6.3 Burst Errors (derived from C1).
5.5.3.6.4SUBC1 correction.
5.5.3.7 If any of the error measurement reveals a sample hold, interpolated or mute level error the tape
should be cleaned and the tape path checked. If after cleaning and repair one or more of the error
rates exceed these thresholds refer to 5.6.3 “Selection of Best Copy.” (above).
5.5.3.8 There are very few error measuring devices available for DAT or other magnetic carriers. Any transfer,
however, should include a measurement of the errors produced at the error correction chip of the
replay machine and this information must be recorded in the metadata of the resultant audio file.
5.5.4.1 Replay equipment must comply with all specific parameters of a given format. Digital tape formats
are mostly proprietary in nature, with only one or two manufacturers of suitable equipment. Latest
generation equipment is preferred, but for older or obsolete digital formats there may be no choice
but to purchase second-hand equipment.
5.5.4.2 The high recording density of R-DAT(Rotary Head Digital Audio Tape) has ensured that applications
other than audio-recording-only were developed. The DDS (Digital Data Storage) format, based
on DAT technology, was developed by Hewlett–Packard and Sony in 1989 and was dedicated to
the storage of computer data. Steady increases in data integrity of the basic system resulted in
developments which allow for signal extraction from audio DAT tapes. Various types of software
are available which allow the extraction of the audio as separate files based on ID’s on the tape.
Dedicated data extraction software can also generate metadata files for each program, including
clock, start and end ID positions, durations, file size, audio properties, etc. Additionally the DDS
format allows double speed capturing of audio material.
5.5.4.3 Nevertheless, the important questions such as format incompatibilities (e.g. the different long play
modes, high resolution recordings, time code extraction etc.), proper data integrity checking,
67
pre-emphasis handling and especially all matters concerning mechanical and tracking problems are
still not yet solved by such systems and therefore need individual treatment.
5.5.5 Common Systems and Characteristics: Cassette Systems
5.5.5.1 The R-DAT (commonly referred to as DAT) is the only common system to use a cassette format
specifically developed for digital audio recordings. DAT tapes have been widely used in field and
studio recording, broadcasting and archiving. New DAT equipment is now virtually unavailable.
Second hand professional DAT machines are a solution, but present maintenance problems as parts
supplies become exhausted.
5.5.5.2 Some last generation recorders operate outside the specification, allowing high resolution recording
at 96 kHz and 24 bits (at double speed), others provided Timecode (SMPTE) recording, or Super Bit
Mapping, a psycho-acoustic principle and critical band analysis to maximize the sound quality of 16-bit
digital audio. 20-bit recordings are quantized to 16 bits using an adaptive error-feedback filter. This filter
shapes the quantization error into an optimal spectrum as determined by the short-term masking and
equi-loudness characteristics of the input signal. Through this technique, the perceptual quality of 20-bit
sound is available on a 16-bit DAT recording. Full quality can only be reached with signals containing
frequencies lower than 5–10 kHz. Super bit mapping does not require special decoding on playback.
Record/playback mode
Standard
Number of
Channels
Sampling rate
(kHz)
Number of
quantization bits
Linear recording
density (KBPI)
Surface recording
density (MBPI2)
Transmission rate
(MBPS)
Sub-code capacity
(KBPS)
Modulation
Correction
Tracking
Cassette size (mm)
Recording time*
(min)
Tape width (mm)
Tape type
Tape thickness
(µm)
Tape speed (mm/s)
Standard Option 1
Option
2
Pre-recorded tape
(Playback only)
Normal
Wide Track
Option 3
track
2
2
4
2
2
2
2
48
44.1
32
32
32
16
(linear)
12 (non
linear)
12 (non
linear)
16 (linear) 16 (linear)
44.1
16 (linear)
61,0
61,0
114
114
2.46
2.46
2.46
1.23
2.46
273.1
273.1
273.1
136.5
273.1
120
240
120
61.1
76
2.46
273.1
8–10 Conversion
Dual Reed Solomon
Area split ATF
73x54x 10.5
120
120
120
3.81
Metal-particle
80
Oxide
13±1µ
8.15
8.15
8.15
4.075
68
8.15
8.15
12.225
13.591
Track pitch (µm)
13.591
Track angle
Standard drum
Drum revolution
speed (r.p.m.)
Relative speed
(m/s)
Head azimuth
6°22’59”5
Ø 30 90° Wrap
2000
1000
2000
3.133
1.567
3.129
20.41 (wide
track)
6°23’29”4
2000
3.133
3.129
±20°
Table 1 Section 5.5 Specifications for various record/playback modes of DAT for both blank and
pre-recorded tapes:
5.5.5.3 Phillips DCC (Digital Compact Cassette) system was (unsuccessfully) introduced as a consumer
product and offered limited compatibility with analogue compact cassettes through the ability to
replay analogue cassettes on DCC equipment. DCC is now considered obsolete.
Format
Variants
DAT or
R-DAT
Timecode is not
part of the R-DAT
standard but may
be implemented in
Sub-Code. Some
pre-recorded DATS
use ME tape.
DCC
Carrier Type
Audio and data
tracks
Digital Audio
Interface
Standards
supported
Cassette
Stereo. Sub16 bit PCM @ 32, AES-422 on
with 3.81mm code includes
44.1 and 48 kHz. professional
metal particle standardised
machines.
tape.
markers plus user
SP-DIF
bits for proprietary
standard.
extensions.
Cassette with Stereo,
3.81 CrO2
metadata standard
supports minimal
descriptive data
PASC compressed
PCM (4:1 bit rate
reduction)
Videotape
based
formats —
see table 4
Table 2 Section 5.5 Digital Audio Cassettes
5.5.6 Common Systems and Characteristics: Open Reel Formats
5.5.6.1 SONY and Mitsubishi have both produced open reel digital systems for the recording studio market,
and NAGRA produced a four-track field recording system, the NAGRA-D.
5.5.6.2 Sony/Studer’s DASH (Digital Audio Stationary Head) system has numerous variants, based on
common formats for the digital tracks on tape. DASH I provides 8 digital tracks on ¼” tape and 24
digital tracks on ½” tape. DASH-II provides 16 digital tracks on ¼” tape and 48 tracks on ½” tape.
Twin DASH formats are commonly used for ¼” stereo digital recordings and utilise twice the normal
number of data tracks for each audio channel to increase the systems error correction capability so
that tape splicing can be used for editing. Low speed formats double recording time by sharing data for
each audio channel across multiple data tracks, halving the number of audio tracks available.
69
5.5.6.3 Nagra still support NAGRA-D Sony DASH and Mitsubishi Pro-Digi format machines are no longer
manufactured. These formats are/were intended for high-end professional use and as a result were
extremely expensive to support.
Format
Carrier
Audio and
Type
data tracks
DASH
Three speeds – ¼” or ½” Up to 48
F (fast),
tape
audio tracks
M (medium) and
plus control
S (slow)
track
DASH-I (single
density) and
DASH-II
(double density)
Two tape widths
Q (quarter inch)
and H (half Inch)
Mitsubishi Pro Stereo
¼” tape
Digi
NAGRA-D
Variants
16 track
½” tape
32 track
1” tape
¼” MP
Digital Audio Standards
Interface
supported
16 bit at 32 kHz, 44.1
AES/EBU
kHz or 48 kHz
SDIF-2
MADI interface
32 kHz, 44.1 kHz or 48
kHz.
20 bit or 16 bit (with
extra redundancy to
facilitate splice editing) at
15 ips.
16 bit (normal
redundancy) at 7.5 ips
32 kHz, 44.1 kHz or 48
kHz.
16 bit
32 kHz, 44.1 kHz or 48
kHz.
16 bit
4 audio tracks. 4 tracks at up to 24 bit
Extensive
48 kHz
metadata
2 tracks at 24 bit 96 kHz
including
TOC and
built-in error
recording
AES/EBU or
proprietary
multi-channel
interface
AES/EBU
Table 3 section 5.5 Open Reel Formats
5.5.7 Common Systems and Characteristics:Video Tape Based Formats
5.5.7.1 There are two variants within this category: systems using videotape in a standard VCR to record
digital audio encoded on a standard video signal, and systems using videotape as the storage
medium for proprietary digital audio signal formats.
70
5.5.7.2 Sony has produced a range of formats using VCR systems as a high bandwidth storage device. More
recently Alesis introduced the ADAT system, which used S-VHS videocassettes as high capacity
storage media for their proprietary format of digital audio, and Tascam released the DTRS system
using Hi8 videocassettes as the storage medium.
5.5.7.3 Formats using video recorders were based on interface devices that incorporated A-D and D-A
converters, audio controls and metering, and the hardware required to encode the digital bit stream
as a video waveform. Sony’s professional system specified NTSC standard (525/60) Black-and-White
U-Matic VCR, and these were manufactured specifically for digital audio use. The semi-professional
PCM-F1, 501 and 701 series worked best with Sony Betamax recorders, but were generally
compatible with Beta and VHS. Machines in this series supported PAL, NTSC and SECAM standards.
5.5.7.4 Reproduction of VCR based recordings requires availability of a VCR of the correct standard, plus
the appropriate proprietary interface. There is normally backwards compatibility within related
systems, so purchase of later generation equipment should facilitate replay of the widest range of
source material. As some of the video based PCM adaptors had only one A/D converter for both
stereo channels, there is a time delay between the two channels. When the tapes are replayed and
the audio data is extracted the signal processor delay should be corrected in the digital domain.
Transfers should be made only with equipment which allows the output of a digital signal.
5.5.7.5 Early digital recorders sometimes encoded in what are now uncommon sampling rates, such as
44.056kHz (see table 4 Section 5.5). It is recommended that the resultant files be stored at the
encoding levels at which they were created. Care should be taken to ensure that automatic systems
do not misrecognise the actual sampling rate (eg a 44.056kHz audio stream may be recognised as
44.1kHz, which alters the pitch and speed of the original audio). Second files can be created for
users in common sampling rates using appropriate sampling rate conversion software. Nonetheless,
the original file should be retained.
5.5.7.6 In addition, third-party equipment for systems based on domestic VCRs can provide useful
extended functionality, including better metering and error monitoring facilities and professional
inputs and outputs.
5.5.7.7 VCR based systems are obsolete, and equipment will need to be sourced second-hand.
71
Format
EIAJ
Sony
PCM-F1
PCM-501
and
PCM-701
systems
Sony
PCM1600
PCM1610
and
PCM1630
DTRS
(1991)
ADAT
(1993)
Variants
Video signal
may be PAL,
NTSC or
SECAM
Carrier Type
Audio and
data tracks
Stereo Audio
Domestic VCR
— normally
Betamax or
VHS cassette
Rare examples
use ½” open
reel videotape
U-Matic – Black Stereo audio
and White,
plus Compact
525/60 (NTSC) Disc PQ
codes
Timecode on
U-matic linear
audio track
Proprietary
format on Hi8
video cassettes
Proprietary
system
on S-VHS
cassettes
Digital Audio Standards
supported
14 bit standard, Sony
hardware allows 16 bit
sampling (with less error
correction)
44.056 kHz in NTSC
systems, 44.1 kHz in PAL
systems
16 bit 44.1 kHz
Interface
Analogue line
in and out
standard. Digital
I/O capability
with third party
add-ons
Sony
proprietary
system. Digital
audio on
separate Left
and Right
Channels plus
word-clock
16 bit 48 kHz
SP-DIF or AES/
20 bit recording optional on EBU
some systems
SP-DIF or AES/
EBU
Table 4 section 5.5 Digital Audio on Videotape — Common Systems
5.5.8 Replay Optimisation
5.5.8.1 Precise identification of the format and detailed characteristics of the source material is essential to
ensure optimum reproduction, and is complicated by the variety of formats with outwardly similar
physical characteristics but different recording standards. Machines should be cleaned and regularly
aligned for best signal reproduction. Any operator-controlled parameters such as de-emphasis must
be set to match the original recording. For VCR based formats the video tracking may need to be
adjusted for best signal, and any dropout compensation on the video signal must be switched off.
5.5.9.1 Misalignment of recording equipment leads to recording imperfections, which can take manifold
form. While many of them are not or hardly correctable, some of them can objectively be detected
and compensated for. It is imperative to take compensation measures in the replay process of
the original documents incurred, as no such correction will be possible once the signal has been
transferred to another carrier.
5.5.9.2 Adjustment of magnetic digital replay equipment to match misaligned recordings requires high
levels of engineering expertise and equipment. The relationship between the rotating heads and the
tape path can be adjusted on most professional equipment, and for DAT recordings especially, this
can lead to significant improvement in error correction or concealment, even making apparently
unplayable tape audible. However, such adjustments require specialised equipment and only trained
personnel should undertake them. Equipment should be returned to correct setting by trained
service technicians after completing the transfer.
72
5.5.10 Removal of Storage Related Signal Artefacts
5.5.10.1It is preferable in most cases to minimise the storage related signal artefacts before undertaking
digital transfer. Digital tapes should be re-spooled periodically if possible, and in any case always respooled before replay. Re-spooling reduces mechanical tension, which can damage the tape base or
decrease performance during replay. Open reel digital tapes that have been left unevenly wound for
some time may exhibit deformations, particular of tape edges, which may cause reproduction errors.
Such tape should be rewound slowly to reduce the aberrations in the wind and rested for some
months, which may aid in reducing replay errors. Though cassette systems can be similarly affected,
the ability to influence the pack through reduced wind speed is not as great with such equipment.
5.5.10.2Magnetic fields do not decay measurably in a period of time that is likely to affect their playability.
The proximity of adjacent tracks or layers will not cause self erasure on analogue tapes, and in the
unlikely event that it may cause issues with older digital tapes this is rarely critical as any resulting
errors are within the limits of the system. Some loss of signal may be measurable in the oldest
video based tapes when used to record digital audio. In these circumstances the lower coercivity of
the magnetic particles and the apparent short wavelength on the tape caused by recording digital
information using a rotating head combine to create the conditions where this may occur, at least
in theory. This may make it difficult for replay equipment to track the information on the tape. All
but the very earliest video tape formulations have a much higher coercivity, combined with systems
which have better error correction technology, which made this problem largely irrelevant. In any
event, attention to the cleanliness of the heads of the replay machine and tape will maximise the
possibility of replay, as will careful alignment of the tape path.
5.5.10.3Seriously damaged tapes may be recoverable using techniques that could be characterised as
“forensic” due to their dependence on high-level skills from a range of scientific and engineering
disciplines (see Ross and Gow 1999). Management of digital tape collections should aim to ensure
copying occurs before un-correctable errors become a problem, as options for restoration of failed
digital tapes are very limited.
5.5.11 Time Factor
5.5.11.1The time needed for copying contents of audio material varies greatly, and is highly dependent on
the nature and status of the original carrier.
5.5.11.2 Preparation time will vary depending on condition of the source copy. Set-up time depends on details
of facilities and formats in use. Signal transfer is generally slightly more than actual running time for each
recoded segment, and time taken for management of metadata and materials management will depend
on details of the archiving system in use. Most audio specific tape based digital recording formats do
not allow upload of the data at greater than real time, with the exception of those mentioned above.
However, capture systems that accurately measure error levels and warn operators when set levels are
exceeded may allow for multiple systems to be run simultaneously.
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5.6 Reproduction of Optical Disc Media (CD and DVD)
5.6.1 Introduction
5.6.1.1 Since their introduction in 1982 replicated optical disc media have become the dominant technology
for distribution of published audio recordings. Recordable optical disc formats, first made available
in the late 1980s1, play an increasingly significant role in distribution and storage of unpublished
audio. Initially marketed as permanent, it has become clear that the usable life of the optical disc is
finite and that steps will need to be taken to copy and preserve their data content. This is especially
the case with recordable disc media, which are not only less reliable than their manufactured
counterparts but are also more likely to contain unique material. Unless recorded and managed
under specified conditions (see Section 6.6 Optical Discs: CD/DVD Recordables), recordable disc
media constitute an unreasonable risk to collection material. This section of the Guidelines concerns
itself with the accurate and efficient copying of CD and DVD optical disc media to more permanent
storage systems. CD is the abbreviation for Compact Disc, DVD initially stood for Digital Video Disc,
then Digital Versatile Disc but is now used without referring to a specific set of words.
5.6.1.2 The Audio CD family may include, in CD-DA format; CD manufactured, CD-R, CD-RW, and in
this form are all characterised by 16 bit digital resolution, 44.1 kHz sampling frequency and 780nm
wavelength read laser. DVD Audio includes SACD and DVD-A. Data formats such as .wav files and
BWF files may be recorded as files on CD-ROM and DVD-ROM. DVD media are characterised by
blue laser around 350 to 450nm for glass mastering and 635–650 nm playback, DVD+R (650 nm),
DVD-R (both for authoring (635 nm laser)). Blu-Ray Discs (BD) are a high definition video and data
format on the same diameter 12 cm disc as DVD and CD. Using a 405 nm blue laser BD is able to
store 25 GB of data per layer.
5.6.1.3 Recordability, rewritability, erasability and accessibility:
5.6.1.3.1 CD and DVD (CD-, DVD-A, CD-ROM and DVD-ROM) discs are pre-recorded (pressed
and moulded) read-only discs. They are neither recordable nor erasable.
5.6.1.3.2 CD-R, DVD-R and DVD+R discs are dye-based recordable (write once) discs, but not
erasable.
5.6.1.3.3 CD-RW, DVD-RW and DVD+RW discs are phase-changed based repeatedly rewritable
discs permitting erasure of earlier and recording new data in the same location on the disc.
5.6.1.3.4DVD-RAM discs are phase-changed rewritable discs formatted for random access, much
like a computer hard disc.
5.6.1.4 The table below (table 1 section 5.6) provides a listing of commercially available CD and DVD
disc types.
1
The first working CD-R system, Yamaha’s PDS (Programmable Disc System), was launched in 1988
74
Disc
Type
Storage
capacity
650 MB
Laser
wavelength
write mode
780 nm
Laser
wavelength
read mode
780 nm
CD-ROM, CD-A, CD-V
read only
CD-R (SS)
CD-R (SS)
write once
write once
650 MB
700 MB
780 nm
780 nm
780 nm
780 nm
CD-RW (SS)
CD-RW (SS)
Rewritable
Rewritable
650 MB
700 MB
780 nm
780 nm
780 nm
780 nm
DVD-ROM, DVD-A,
DVD-V:
SS/SL
SS/DL
DS/SL
DS/DL
read only
650 nm
650 nm
DVD-R(G)
write once
4.7 GB
650 nm
650 nm
DVD-R(A)
SL
DL
write once
3.95 or 4.7
GB
8.5GB
635 nm
650 nm
write once
4.7 GB
8.5 GB
650 nm
650 nm
DVD-RW
Rewritable
4.7 GB
650 nm
650 nm
DVD+RW
Rewritable
4.7 GB
650 nm
650 nm
DVD-RAM
SS
DS
rewritable
650 nm
650 nm
HD-DVD –R
SL
DL
HD-DVD –R W SL
DL
BD-R
SL
DL
BD-RE
SL
DL
write once
2.6 or 4.7
GB
5.2 or 9.4
GB
15 GB
30 GB
15 GB
30 GB
25 GB
50 GB
25 GB
50 GB
405 nm
405 nm
405 nm
405 nm
405 nm
405 nm
405 nm
405 nm
DVD+R
DL
SL
4.7 GB
8.54 GB
9.4 GB
17.08GB
rewritable
write once
rewritable
Typical use
Commercially
available
Music recording,
computer data, files,
applications
Computer data
recording, files,
applications
Movies, interactive
games, programmes,
applications
General use: One
time video recording
and data archiving
Authoring/
professional use
Video recording and
editing
General use: One
time video recording
and data archiving
General use: Video
recording and PC
backup
General use: Video
recording and editing,
data storage. PC
backup
Computer data:
Storage repository for
updateable computer
data, back-ups
data and highdefinition video
Table 1 Section 5.6 Commercially available CD/DVD disc types
SS= Single-sided, SL=Single layer, DL=double-sided, DL=dual layer
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5.6.1.5 Under optimum conditions digital discs can produce an unaltered copy of the recorded signal,
however, in the case of audio specific recordings, any un-corrected errors in the replay process will be
permanently recorded in the new copy, or sometimes unnecessary interpolations will be incorporated
into the archived data, neither of which is desirable. Optimisation of the transfer process will ensure
that the data transferred is most closely equivalent to the information on the original carrier. As a
general principle, the originals should always be kept for possible future re-consultation, however, for
two simple, practical reasons, any transfer should attempt to extract the optimal signal from the best
source copy. Firstly, the original carrier may deteriorate, and future replay may not achieve the same
quality, or may in fact become impossible, and secondly, signal extraction is such a time consuming
effort that financial considerations call for an optimisation at the first attempt.
5.6.2 Standards
5.6.2.1 Compact Disc Standards: The standard for CD was originally a product of the companies Philips
and Sony. The standards are named after a colour, the first being the Red Book: Philips–Sony Red
Book CD Digital Audio, also includes CD Graphics, CD (Extended) Graphics, CD-TEXT, CD-MIDI,
CD Single (8cm), CD Maxi-single (12cm) and CDV Single (12cm). Yellow Book standard specifies
the CD as a data file carrier, the Green Book describes CD-I or interactive data, Blue Book describes
Enhanced (multimedia) CD, and White Book specifies CD-V (video) characteristics. Orange Book is
the standard that refers to Recordable and Rewritable CDs (and is described more fully in Chapter
6). The colour book standards, subject to certain limitations, may be ordered from the Philips web
site at http://www.licensing.philips.com/. They are primarily intended for manufacturers. The ISO
standards which describe CDs are purchasable from International Standards Organisation (ISO)
Central Secretariat http://www.iso.org/. IEC 908:1987, Compact Disc Digital Audio System (CD-DA)
(n.b. IEC 908:1987 and Philips-Sony Red Book are basically equivalent.) ISO 9660:1988, Volume and
File Structure (CD-ROM) (ECMA-119) and ISO/IEC 10149:1995, Read-Only 120 mm Optical Data
Discs (CD-ROM) (ECMA-130).
5.6.2.2 DVD Standards: There is an extensive range of ISO standards for DVD. However, similarly to
CD, there are also proprietary versions of the standards. These standards are referred to by an
alphabetical appellation: DVD-ROM, the basic data standard, is specified in Book A, DVD video is
described in Book B, DVD-Audio in Book C, DVD-R in Book D, and DVD-RW in Book E. The ISO
standards are purchasable from International Standards Organisation (ISO) Central Secretariat
http://www.iso.org/ ISO 7779:1999/Amd 1:2003 Noise measurement specification for CD/DVDROM drives. ISO/IEC 16448:2002 Information technology -- 120 mm DVD -- Read-only disc and
ISO/IEC 16449:2002 Information technology -- 80 mm DVD -- Read-only disc.
5.6.3.1 Unlike copying analogue sound recordings, which results in inevitable loss of quality due to
generational loss, different copying processes for digital recordings can have results ranging from
degraded copies due to re-sampling or standards conversion, to identical “clones” which can be
considered even better (due to error correction) than the original. In choosing the best source
copy, consideration must be given to audio standards such as sampling and quantisation rate and
other specifications including any embedded metadata. Also, data quality of stored copies may have
degraded over time and may have to be confirmed by objective measurements. If there is only one
copy in poor physical condition in a collection, it may be wise to contact other sound archives to
determine whether it is possible to find a better preserved copy of the same item.
76
5.6.3.2 As a general rule, a source copy should be chosen which results in successful replay without errors,
or with the least errors possible. Replicated discs are more stable than recordable media and would
normally be preferred if a choice is available. Physical condition may provide an indication of quality,
however the only certain method for choosing an error free disc is to institute routine error checking
and reporting as part of the transfer process. Even with error checking and reporting, the extraction of
best possible signal is problematic as the lack of standards with drives means that different players may
produce different results on the same disc (see 8.1.5 Optical Discs — Standards). As with all digital to
digital transfers, an error status report must be made and incorporated in the administrative metadata
of the digital archive file, along with a record of the drive used.
5.6.4 Playback Compatibility
5.6.4.1 The variety of standards and the manner in which they may be encoded makes selection of the
correct replay equipment necessary. The domestic freestanding CD player, for instance, will most
likely only play CD-Audio and its variants, whereas the CD-ROM drive in a computer will play all the
formats, though it requires the appropriate software to determine the content. DVDs will not play in
CD drives or players, although many DVD drives are compatible with CDs.
5.6.4.2 The tables below lay out the compatibility between certain drives and their appropriate media.
Disc type
CD-ROM
CD-R
CD-RW
CD-ROM drive
Read
Write
Yes
Yes
Yes
No
No
No
CD-RW or CD-R/RW drive,
Read
Write
Yes
Yes
Yes
No
Yes
Yes
CD-R Drive
Read
Write
Yes
Yes
Yes
No
Yes
No
Table 2 Section 5.6 Read Write Compatibility; CD
Disc type
Home
DVD-ROM
DVD-R DVD-R (A) DVD-RW
DVD+
DVD-RAM
DVD
drive
(G) drive
drive
drive
RW/+R drive
drive
player
Play only
Records
Records
Records
Records
Records
Play only (Computer) General -R Authoring -RW, General +RW, +R
RAM
-R
-R
DVD-ROM
No
No
No
No
No
No
No
DVD-R(A)
No
No
No
Yes
No
No
No
DVD-R(G)
No
No
Yes
No
Yes
No
No
DVD-RW
No
No
No
No
Yes
No
No
DVD+RW
No
No
No
No
No
Yes
No
DVD+R
No
No
No
No
No
Yes
No
DVD-RAM
No
No
No
No
No
No
Yes
CD-ROM
No
No
No
No
No
No
No
CD-R
No
No
Yes
No
Yes
Yes
No
CD-RW
No
No
No
No
Yes
Yes
No
Table 3 Section 5.6. Compatibility; DVD (Write Mode).
77
Disc type
Home
DVD
player
Play only
DVD-ROM
Not
Yes
Yes
Yes
Yes
Usually
Mostly
Usually
Yes
Yes
Yes
Yes
Yes
Mostly
Usually
Yes
Yes
Yes
Yes
Yes
Partly
Usually
No
Yes
Yes
Usually
Usually
Partly
Usually
Usually
Usually
Usually
Yes
Usually
Partly
Usually
Usually
Usually
Usually
Yes
Usually
Rarely
Rarely
No
No
No
No
Yes
Depends
Yes
Yes
No
Yes
Yes
Usually
Usually
Yes
Yes
No
Yes
Yes
Usually
Usually
Yes
Yes
No
Yes
Yes
Usually
All DVD drives should play DVD-Audio or DVD-Video if the computer has DVD-Audio or
DVD-Video software installed. DVD-RAM drives are questionable.
DVD-R(A)
DVD-R(G)
DVD-RW
DVD+RW
DVD+R
DVD-RAM
CD-ROM
CD-R
CD-RW
DVDAudio
DVDVideo
DVD-ROM
drive
Play only
(Computer)
DVD-R
(G) drive
Records
General -R
DVD-R (A)
drive
Records
Authoring
-R
Yes
DVD-RW
drive
Records
-RW, General
-R
Yes
DVD+
RW/+R drive
Records
+RW, +R
DVD-RAM
drive
Records
RAM
Table 4 Section 5.6. Compatibility; DVD (Read Mode).
5.6.5 Cleaning, Carrier Restoration
5.6.5.1 CDs or DVDs do not require routine cleaning if carefully handled, but any surface contamination
should be removed before replay or in preparation for storage. It is important when cleaning
to avoid damaging the disc surface. Particulate contamination such as dust may scratch the disc
surface when cleaning, or use of harsh solvents may dissolve or affect the transparency of the
polycarbonate substrate.
5.6.5.2 Use an air puffer or compressed clean air to blow off dust, or for heavier contamination the disc
may be rinsed with distilled water or water based lens cleaning solutions. Care should be taken
as the label dyes in many CD-Rs are water soluble. Use a soft cotton or chamois cloth for a final
wipe of the disc. Never wipe the disc around the circumference, only radially from the centre to
the outside of the disc – this avoids the risk of a concentric scratch damaging long sections of
sequential data. Avoid using paper cleaning products or abrasive cleaners on optical discs. For severe
contamination isopropyl alcohol may be used if required.
5.6.5.3 It is preferable that no repairs or polishing is undertaken on archival optical discs as these processes
irreversibly alter the disc itself. However, if the disc surface (reading side) shows scratches that
produce high level errors, repairs which return the disc to a playable state may be allowed for the
purposes of transfer. These may include wet polishing systems providing careful testing of the effect
of these restoration systems have been undertaken before being applied to important carriers.
This should be undertaken by testing an expendable disc, undertaking the restoration process, and
retesting to determine the effect of restoration (for further details consult ISO 18925:2002, AES
28–1997, or ANSI/NAPM IT9.21 and ISO 18927:2002/AES 38– 2000). Though some initial testing
of wet polishing indicates adequate results, the removal of surface material makes sound archivists
78
reluctant to endorse this approach. Moreover wet polishing is only effective with small scratches;
discs with deep scratches deliberately inflicted with, for example a knife or scissors, will not be
returned to playability by wet polishing. Damages on the label side will not benefit from any repair
measures described.
5.6.5.4 Before and after cleaning and/or repairing measures and prior to the reproduction it may be
advisable to first measure the CD’s or DVD’s error rates, as a minimum:
5.6.5.4.1 Frame burst errors (FBE) or Burst Error length (BERL)
5.6.5.4.2 Block error rate (BLER)
5.6.5.4.3 Correctable errors (E11, E12, E21, E22, errors before interpolation)
5.6.5.4.4 Uncorrectable errors (E32)
And preferably:
5.6.5.4.5 Radial noise and tracking error signals (RN)
5.6.5.4.6 High frequency signals (HF)
5.6.5.4.7 Dropouts (DO)
5.6.5.4.8 Focusing errors (PLAN)
5.6.5.5 There are a range of error measuring devices available for CD and DVD of varying sophistication,
accuracy, and cost. A reliable tester is, however, a necessary part of a digital disc collection to
determine if critical error thresholds are exceeded (cf 8.1.5 Optical Discs — Standards and
8.1.11 Testing Equipment). If after cleaning and repair one or more of the error rates exceed these
thresholds refer to 5.6.3 “Selection of Best Copy”.
5.6.6.1 There are two fundamentally different approaches to reproduction of audio CD and DVD sources:
traditional replay using format-specific reproduction equipment; or digital audio extraction (DAE)
using a general purpose CD-ROM or DVD-ROM drive, commonly referred to as “ripping” or
“grabbing”. The chief advantage of the data capture or ripping method is greater speed, for while
traditional reproduction requires transfer in real time, data capture or “ripping” utilising high speed
drives can easily transfer audio data in less than one tenth of the actual audio running time.
5.6.6.2 Digital Audio Extraction: The chief disadvantage of DAE is in error handling. The simplest “ripping”
software has no error correction capability at all. More sophisticated systems make some attempt
at error management but do not have the functionality to fully implement the error checking,
correction and concealment that is necessary for accurate transfer, and which is built into format
specific equipment. Top end professional systems promise error handling equivalent to the format
specific approach, yet few have accurately implemented it.
5.6.6.3 Reproduction at rates significantly faster than real time are desirable in that this reduces the
resources required to transfer audio material to the target archival system. If the DAE system can
be automated, this has the added advantage of freeing staff resources for the more human resource
intensive tasks of converting analogue audio to digital. Automated systems can be used appropriately
if there is no loss of accuracy in the transfer process. In fact, in the better systems, there is less
danger of data inconsistencies, particularly those affecting metadata but also possibly affecting the
content itself.
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5.6.6.4 Reproduction of digital audio data should always be accompanied by an accurate error detection
and recognition system that describes and identifies exactly the kind and number of CD-specific
errors and associates them with the metadata specific to that audio file. This is all the more critical
where automated, faster-than-real-time processes are used to acquire the audio data.
5.6.6.5 The reproduction of an audio CD is a unique process where a somewhat subjective decision needs
to be made about the success, or otherwise, of the transfer process. Unlike the transfer of audio
data files, this decision can only be made by considering the error protocol. Data formats, such
as .wav or BWF, can be objectively checked by bit for bit comparison between the new and old
files. CD audio is not a digital file, but a coded stream of audio data, a significant difference when it
comes to managing the audio integrity.
5.6.6.6 Systems which guarantee error detection and recognition including error protocol in a faster-thanreal-time mode up to a maximum of 12 times, relative to real time audio replay, are available on the
market and are generally specifically aimed at the archival market.
5.6.6.7 The minimum requirement for archival use of DAE is that the DAE system must detect and alert
the operator to any digital audio errors.
5.6.6.8 Format Specific Replay Approach: To transfer a CD encoded in CD-A format a stand-alone CD
player may be used. The required replay equipment is a CD player with digital output, permitting
ingest of the digital audio stream via a sound card with digital input. Preferred interface standard
for the digital audio stream is AES/EBU. Use of the SPDIF interface can provide the same results
but cable runs must be kept short. Any conversion between AES/EBU and SPDIF needs to
accommodate the differences between the two standards, notably the different use of status bits
that carry emphasis and copyright flags (Rumsey and Watkinson 1993). The disadvantage with this
real time replay approach is that it is very time consuming, and no record of error correction is
maintained in the record metadata.
5.6.6.9 Sound cards for ingest of CD audio must accommodate two channels at 16 bit 44.1 kHz. Replay
equipment should be of commercial quality. Care taken in ensuring a stable vibration free mounting
for the player will ensure maximum reliability of replay.
5.6.6.10The CD player must be in good replay condition. In particular, optimum laser power is mandatory,
and the laser lens should be cleaned from time to time. Devices such as disc-tuners are of no use
to any replay of a CD. It is advised against using protective foils (so called CDfenders/ DVDfenders)
because they may come off from the disc and damage the drive2.
5.6.7 Issues with DVD Audio (DVD-A)
5.6.7.1 DVD audio delivers 6 channels of audio at the 24 bit 96 kHz standard, and/or two channels at 24 bit
192 kHz, however digital outputs on most DVD players are limited to 16 bit 48 kHz resolution as
a piracy control measure. The DVD forum has selected IEEE1394 (firewire) as the preferred digital
interface for DVD Audio, using the “Audio and Music Data Transmission Protocol” (A&M protocol)
(http://www.dvdforum.com/images/guideline1394V09R0_20011009c.pdf).
5.6.7.2 Decoding compressed formats such as MLP can be done by the player or at a later processing stage.
Discs may include alternative versions or additional content including down mixing of surround
2 CDs aus dem Kühlschrank. Funkschau no. 23, 1994, p.36–39. The effect of improving the replay quality of CDs or DVDs by cooling
them down in a refrigerator is so minute that though it was shown in theory (mathematically) it has never been shown in practice
80
signals to stereo, alternative tracks, accompanying video etc, requiring a policy decision as to whether
all these versions are to be collected or if not which alternatives are required for the archive. It is
also important that archive staff be aware that hybrid discs, such as those recorded in compliance
with the Blue Book standard as Enhanced CDs, may contain other data. The extra graphical or
textual data may be critical components of the work and are therefore necessary in acquiring and
preserving the content.
5.6.8 Issues with Super Audio CD (SACD)
5.6.8.1 The SACD format is based on Direct Stream Digital (DSD), a 1 bit sampling technique at 2.8 MHz
sampling frequency which is not directly compatible with linear PCM. At the time of writing there
are limited options for ingesting this type of signal into a digital audio storage system, as most SACD
players do not provide either an SACD bitstream output or a high quality PCM signal derived from the
bitstream. Sony has its proprietary I-Link interface using firewire, and some third party manufacturers
have marketed proprietary interfaces that can handle SACD in its native format, but there is no
widely accepted digital interface standard for this format. Indications are that a suitable open standard
protocol for transmission of SACD over IEEE 1394 firewire though promised, may never eventuate.
5.6.8.2 Workstations developed for SACD mastering have capabilities for input, output and processing of
DSD signals (http://www.merging.com/). It should be noted that even basic processing such as gain
adjustment of DSD or SACD streams requires a completely different computational approach, and
therefore very different algorithms to that of PCM, consequently, the restoration and re-use of audio
encoded into such formats will be limited unless converted to PCM.
5.6.9 Time factor
5.6.9.1 Time required for ingest of the audio data from optical disc in real time for conventional replay
approaches a factor of two for every hour of audio. DAE approaches may reduce this by around a
factor of 10, and an automated juke box system will load 60 or more CDs in a few hours without
staff resources beyond the initial loading. Additional time must be allowed for selection of best
copies, re-copying in the case of unacceptable errors, plus file and data management.
5.6.10 Minidisc
5.6.10.1 The original Minidisc (MiniDisk, MD) appeared in two forms: as a mass replicated disc, which works
according to the principles of optical discs, and as a recordable, actually rewritable, disc, which is a
magneto-optical recording medium (cf Section 8.2 Magneto Optical discs). Both sub-formats may be
read by the same players. The discs are of 2.5” (64mm) diameter and housed in a cartridge. Minidisc
recordings employ Adaptive Transform Acoustic Coding (ATRAC), a data reduction algorithm based
on perceptual coding. Data reduced formats, although highly developed (at least in the later versions
of ATRAC), not only omit data irretrievably that would otherwise be captured by a non-data reduced
format, but also create artefacts in the time domain as well as in the spectral domain. Such artefacts
can lead to misinterpretations of spectral components as well as of time-related components,
especially when analysing the signal by means of a spectral tool. The artefacts of data reduction codecs
cannot be recalculated or compensated for at a post processing stage, as they are dependant on the
level, dynamics and frequency spectrum of the original signal. ATRAC is a proprietary format, with
many versions and variations, and for archival purposes it is advisable to re-encode the resultant files of
compressed recording formats as .wav files.
81
5.6.10.2Many minidisc players have digital output which will allow the production of “pseudolinarised” data
stream. The resultant file should comply with specifications laid out in chapter 2 Key digital principles
and stored in accordance with that section. Metadata about the origin of such signals are imperative,
as pseudolinearised signals cannot be distinguished from signals recorded without data reduction.
This information would be recorded in the coding history of a BWF file, or be rendered as change
history as per PREMIS recommendations (see Chapter 3 Metadata).
5.6.10.3In 2004 the Hi-MD was marketed, and it incorporated changes to hardware which, with the new
media, would record up to 1 GB of audio data. With Hi-MD it was possible to record several
hours of data reduced signals, but more importantly, it was also capable of recording linear PCM
signals. For archival purposes these recording should be treated like CD signals and transferred as a
data stream to a suitable file storage system. Extracting audio data directly from HD-MD at higher
transfer rates requires specific proprietary software, some of which is available from manufacturers’
websites. It is advisable to purchase dedicated replay equipment and software immediately as
prolonged manufacturer’s support cannot be guaranteed.
5.6.10.4The use of Minidisc as an original recording machine is not recommended (see section 5.7 Field
Recording Technologies and Archival Approaches).
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5.7 Field Recording Technologies and Archival Approaches
5.7.1 Introduction
5.7.1.1 Many collections are created through programs of field recording rather than, or perhaps in addition
to, the acquisition and preservation transfer of historic recordings to stable digital storage formats
and systems. These field recordings may be used in the creation of oral history collections, programs
of traditional and other cultural performance, environment and wildlife recordings, or as part of the
responsibility of broadcast collections. Regardless of the subject matter, where these recordings are
destined for long term retention in archival collections it is most effective to make a decision about
matters relating to their archival life at the time of planning the recording. In fact, inappropriate
formats and technologies can severely limit the life and usability of the resultant audio.
5.7.1.2 Field recording may be undertaken in a variety of locations and situations, and the subject of such
recording may be anything that makes a sound; from people, technology, plants or animals, to the
environment itself. Recordings may be made to capture the acoustic context, i.e. in which the
desired sound is recorded in an acoustic environment, or may be isolated from it, in which the
recording technology may be deployed in a way which minimises the environment in which the
recording is made. Recordings may be made in lounge chairs in big cities, on the verandas of remote
bungalows, or where there is neither technology nor society to support it. The possibilities are
virtually limitless and consequently this chapter on field recording technologies does not seek to
discuss the specific discipline-related details of field recording techniques. Rather, it answers a simple
question: “How do you best create a sound recording in the field in which the content is intended
for long term archival storage?”
5.7.1.3 This subject of this section falls somewhat between the previous chapters on signal extraction, and the
following chapters on digital storage technologies. It is included here, as it addresses the creation of
digital audio content which is ingested into the digital storage systems as per the following chapters.
5.7.2 Field Recording Standards
5.7.2.1 The same technical recording standards apply to field recordings as they do to archival transfers;
i.e. they should be captured and stored in a widely used, standard linear audio file format, normally
.wav or BWF .wav format; they should be created with a suitable sampling rate; at least 48 kHz, but,
depending on intentions, possibly higher, either 96 kHz or maybe in some circumstances 192 kHz or
higher. It is advisable to make recordings at 24 bit. Lower rates will not reflect the dynamic range of
the performance and the environment in which the recording is made and could well result in low
level signals of very poor quality.
5.7.2.2 Whatever the recording resolution, it is advisable to record natively to a standard format. This
allows direct transfer to archival storage without alteration of the format and simplifies the archiving
processes. Using BWF facilitates the collection of critical metadata which is necessary to the life
cycle of archival digital information.
5.7.2.3 The use of data reduced (popularly called compressed) recording formats, such as MP3 or ATRAC
encoding will produce recordings which do not meet archival standards. Data reduced formats,
although highly developed, not only omit data irretrievably that would otherwise be captured by
a non-data reduced format, but also create artefacts in the time domain as well as in the spectral
domain. Such artefacts can lead to misinterpretations of spectral components as well as of time-related
components, especially when analysing the signal by means of a spectral tool. The artefacts of data
reduction codecs cannot be recalculated or compensated for at a post processing stage, as they are
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dependant on the level, dynamics and frequency spectrum of the original signal. For archival purposes
it is advisable to re-encode the resultant files of compressed recording formats as .wav files (this is also
the case with Minidisc, and early technology which used lossy codecs (See 5.6.10 Minidisc). While this
does not replace the missing data, it does reduce further dependence on the codecs.
5.7.3 Selection of Recording Equipment
5.7.3.1 The decision about the use of a particular piece of recording equipment depends on many matters.
There are, however, a number of technical issues common to all field recording situations and these
can be grouped under three headings: archival compatibility, audio quality, and reliability.
5.7.3.2 Archival compatibility
5.7.3.2.1 The choice of the recording format in the digital domain has a long, and irreversible,
impact on archival life: e.g. lossy compression formats may reduce particular usages. For
this reason the recording device should be chosen according to the archival compatibility
of its recording format. Current technology offers the possibility of recording directly to
a file based format using hard disk and solid state recorders. Such devices usually provide
a choice of several linear and data reduced recording formats. The selection of .wav or
BWF .wav is recommended. Raw or proprietary formats should be avoided as these often
have to be transferred to .wav or BWF .wav via proprietary software for future long term
archiving. In keeping with archival recommendations, data reduced recording formats should
not be used.
5.7.3.2.2 An alternative to dedicated portable recorders is a suitably equipped laptop computer.
With the addition of a high quality microphone pre amp and analogue to digital convertor
(see Section 2.4 Analogue to Digital Converters (A/D)) sound can be directly recorded to
a laptop using widely available recording software. The same recommendations regarding
file format applies to laptops as well, i.e. it is generally best to record directly in the storage
format. This solution is practical, but high power consumption, as well as the acoustic noise
which may be generated by the laptop itself, and the conspicuousness of the computer
make this suitable for only some situations.
5.7.3.2.3 The laptop, and many of the portable recording devices, can be configured to record
simultaneously to an external hard disk. This additional safety strategy is outlined in 5.7.5.1
(Transfer and Backup of content in the Field).
5.7.3.3 Audio quality
5.7.3.3.1The audio quality should be chosen according to archival recommendations in Chapter 2,
Key Digital Principles. The requirement for good quality recording applies to all types of
content. Contrary to widespread opinion, spoken word recordings benefit from the same
high resolution as music recordings, in fact it may be argued that the dynamics of speech
places more demands on recording technology than many forms of music. In addition,
if detailed signal analysis (e.g. formant / transient consonant analysis etc.) is required, the
higher quality is a necessity.
5.7.3.4 Microphones
5.7.3.4.1The discussion below regarding microphones is limited to issues related to the creation of
archival recordings. Much more can be said about microphones as these are, in essence, the
tools used in the most creative and manipulable part of the process and it is recommended
that any field recordist be familiar with the use of microphones.
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5.7.3.4.2The use of external microphones, separate from the recorder, is recommended in the
majority of recording situations. This minimises the inherent system noise captured by inbuilt
microphones, and avoids handling noise when operating the recorder. The quality of the
microphones should be sufficient to match the needs of the recording task as well as the
specifications of the recording device, noting especially the signal to noise ratio (SNR). In
order to capture the full dynamic range possible, and hence record 24 bit recordings, the use
of good quality external microphones with a suitable preamplifier are necessary as most of
the lower quality recording devices and microphones compromise at this crucial point.
5.7.3.4.3 In some recording situations the positional characteristics associated with the event
are important. To capture such information a pair of external microphones deployed in
a standard array is required (see Section 5.7.4.3 below). A standardised microphone
array will provide comprehensible stereo sound characteristics whereas fixed internal
microphones, as provided by many devices, usually do not match any standardised
microphone array and are not manipulable. Condenser microphones are the most sensitive,
and generally preferred for best recording results. Condenser microphones need phantom
power which is normally provided by a professional recording device, (ideally switchable)
but can also be provided by an external battery or mains powered supply. Condenser
microphones tend to be more likely to be damaged in poor conditions and it may be
preferable to trade off sensitivity and use more robust microphones such as dynamic
microphones in some situations. Condensor microphones are also quite expensive, and
very good results can be achieved with some of the higher quality electret-condenser
microphones which, having a permanently charged capsule, can operate for extended
periods of time on a small battery. Outdoor recording, especially with condenser or
electret-condenser microphones, requires adequate high quality wind shields. Incorrect and
ad hoc wind shields can be detrimental to the recording characteristics and alter the polar
patterns of the microphones making the recording less predictable. Users should be aware
of this effect when selecting and using windshields.
5.7.3.5 Reliability
5.7.3.5.1Unreliable equipment has the potential to lose already recorded material or fail just when it is
required for a recording. To minimise the risk of failure, recording equipment should be chosen
to give the best possible reliability. Low cost consumer-grade devices are in many cases, flimsy
and insubstantial, and easily subject to damage, and should not be used in the field before
being extensively tested. In addition to more robust construction professional devices offer
more reliable circuitry and interfaces, such as balanced microphone inputs, and so allow
long cable runs and more reliable professional connectors. Even though low cost equipment
is more likely to be susceptible to damage and failure, cost should only be an indicator of
reliability and all field equipment should be tested extensively before being used in the field.
5.7.3.6 Testing and maintenance
5.7.3.6.1Regardless of cost or quality, all recording equipment should be regularly tested and
maintained to ensure accurate and reliable functionality especially under field conditions.
The integrity of the recording system should be tested, especially after equipment has
been dropped or transported under irregular conditions. The frequency response of
microphones should be regularly measured to ensure they are functioning adequately.
Dust and humidity protection is vital in keeping equipment in good working condition.
Regular checking and cleaning of the devices, including connectors and other surfaces is vital
to maintaining a reliable recording device. Equipment should be allowed to acclimatise to
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changing environmental conditions, especially when moved from a cool dry environment,
such as a plane’s cargo hold, to a hot humid environment. All test results should be kept
to allow the production of a continuous report of the maintenance condition of field
equipment and to foresee necessary exchange of components.
5.7.3.7 Other considerations for field recording equipment
5.7.3.7.1Though the technical specifications and characteristics help determine the quality and
reliability of a recording device, other practical issues can impact on the choice of equipment
according to the envisaged recording situation. Important features include; adequate recording
time when battery-supplied; a rugged and clear design; easy handling; and a small and lightweighted but robust construction. Illuminated controls are essential for recording in the dark
but result in higher battery consumption. A decision should be made as to whether the
recording situation makes devices with changeable media (such as Flash or SD cards) or a
back up hard disk preferable to enable a suitable safety strategy (see Section 5.7.5 Transfer
and Backup of content in the Field). Ideally the device should allow fast and simple data
transfer and duplication, and have an inconspicuous design (the latter of which reduces the
visual impact on a documentary recording, and may also minimise the risk of theft).
5.7.4 Approach to recording
5.7.4.1 The purpose of the recording and the rules of the particular discipline to which it belongs will
govern many aspects of recording approaches, microphone techniques and the like. There are,
however, a number of common concerns in making such a recording.
5.7.4.2 Field recordings usually record or document a given situation and under these circumstances the
original dynamics of the documented action should be respected in the recording as well. Audio
input levelling should orientate on the wanted signal, and not the general background noise, and
continuous adjustment of the level during a recording should be done judiciously, if at all. Use of
automatic gain control functions is not recommended as such features falsify original dynamics by
raising low level parts (and therefore noise) and reducing the wanted signal dynamics. Likewise
any limiters used in a recording should be applied cautiously. A well adjusted limiter will rescue
the recording if an unexpected high level signal is captured but have absolutely no impact on the
majority of the recording because it is not triggered by the level of the recording. On the other
hand, a poorly adjusted limiter may simulate a perfect level on the meters of the recording device
while the microphone itself may already be overloaded due to the input signal. Whenever possible,
manual levelling is to be preferred and any limiter, adjusted so as it has no impact on the normal
signal, only switched in after an optimum level has been achieved.
5.7.4.3 When making a recording where the signal is embedded in a noisy environment advantages are to
be found in using standard stereo microphone arrays. There are many approaches but those that are
briefly discussed here include near-coincident technique of which ORTF (Office de Radiodiffusion
Télévision Française) is an example, XY crossed pair, AB parallel pair and MS (Mid-Side) techniques.
5.7.4.4 ORTF seems to be most useful where analysis and evaluation properties of the documentary
recording are an important requirement. In this technique the microphone capsules are separated
by 17cm at an angle of 110°. An ORTF recording, when analysed via headphones, enhance the ear
and brain’s ability to trace a wanted signal within a noisy surrounding; the so called “cocktail party
effect”. The head-related binaural microphone array imparts the extra information and so helps
identifying wanted signals in noisy sound fields. Also, as the specification for ORTF is defined, the
microphone set-up can be much more easily replicated in a standard way.
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5.7.4.5 Standard XY crossed pairs are arranged so that the microphone capsules are as close together
as possible, but pointing at least 90° away from each other. The intensity of the signal information
is recorded, but ideally no phase difference is noted. This technique produces a recording that
reproduces well on speakers, but does not have as much separation information as other
techniques. AB parallel pair uses two omni-directional microphones in parallel separated by around
50cm. This technique has been favoured in very good acoustic environments but will rarely produce
acceptable results in very noisy environments. It may have phase cancellation problems when
summed to mono.
5.7.4.6 MS (Mid-Side) technique places a bidirectional microphone (figure 8) at right angles to the sound
source, and a cardioid pick up pattern microphone (or sometime an omni directional microphone)
pointing at the sound source. The two recorded signal may then be manipulated to produce mono
compatible stereo recording (M+S, M-S). If recorded as MS information, the signal may also be
manipulated after the event, and so gain some control over the apparent spread of microphones.
5.7.4.7 Some situations, where the exact nature of the event is unknown prior to the recording being made,
can take advantage of movable directional microphones, multi-microphone techniques and multitrack recording. Interviews may use two microphones pointed at the participating individuals, which
presents very acceptable recordings. Clip microphones are, in many cases, less useful, as they pick
up unwanted noise from body movements, breathing, clothing and jewellery, and record little or no
information about the environment in which the recording was made, which is often an integral and
necessary part of the field recording.
5.7.4.8 Microphone techniques contribute to the quality of the recorded content and this very brief
consideration of them is only a guide to the possibilities. It is recommended that all those intending
to make recordings in the field should become familiar with the possibilities afforded by good
microphone techniques before making important recordings.
5.7.5 Transfer and Backup of content in the Field
5.7.5.1 Field recordings remain vulnerable while in the field, and unless back up copies are created, are at
risk of being lost. A second copy of a field recording should be made at the time of recording or
as soon as possible after the recording is completed. Different workflows and situations make for
different approaches, but generally speaking, the workflow selected should offer the best possible
safety strategy.
5.7.5.2 Hard disk and solid state recorders offer a file based recording technology either on hard disks or
on changeable card media. The recording is generally deleted from either of these media after the
wanted file is transferred to another storage environment. This is clearly an area of risk in the use
of the new technology and must be managed carefully to ensure no loss of wanted material. The
recording medium should be regarded as an original carrier as long as possible. It should be erased
only after verifying the correct data transfer into an archival system. In the case where a long field
trip requires the management of large amounts of data which cannot be immediately archived,
duplicates should be created and stored in the field. In the case of flash card or SD recorders it
may be useful to invest in additional storage cards which are used to store recording until recorded
content is transferred to a more sustainable storage system. In the case of hard disk or laptop
recording devices, portable hard disk storage devices can be used to create backup copies until the
data has been successfully transferred.
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5.7.5.3 In practice, some devices offer parallel use of internal hard disk and storage cards, or allow the
parallel recording to hard disk. This is an advantage as it enables the automatic creation of a safety
copy as part of the recording process and should be undertaken whenever possible. Alternately,
safety copies can be manually created in the field, using external hard disks, laptops or at least CD/
DVD drives.
5.7.5.4 Some devices create file names automatically when a new storage medium is inserted (automated
numbering starting with the same file name on each new medium), so the copy process has to
be carefully managed to be sure that files named the same on different carriers can be correctly
matched with the correspondent metadata/ field notes etc. In the worst case this can lead to
accidental erasure of identically named files and so a careful structure and naming strategy is
necessary. Renaming the files after the copy process is recommended, provided that the original file
is not changed or manipulated in some other way.
5.7.6 Metadata and Collection Description
5.7.6.1 The absence of metadata describing the field recording, its context and related rights, severely limits
the value of the recording. The lack of metadata (including preservation metadata) can have serious
implications not only for ingestion into a repository, but also for subsequent archival management
and dissemination of archival information. This data is so significant that its lack may lead an archives
manager to reject the content. There is also critical technical and preservation information necessary
to acquiring field recordings which should be obtained at the time of recording and included in the
archival record. These include:
5.7.6.1.1 Recording device: Brand, model number, description of dynamically made adjustments
during the course of the recording, recording level, recording format, encoding (not
recommended but should circumstances require its use, it must be documented).
5.7.6.1.2 Microphones: microphone types/ polar pattern, information about the microphone array,
distance, special approach (like clip microphones, analytic multi microphone technique etc).
5.7.6.1.3 Use of additional equipment such as windshields etc. description of room situation, etc.
5.7.6.1.4 Carrier: type, specifications of original carrier (flash card, disk etc) or hard disk.
5.7.6.1.5Power source: batteries, 50 or 60 Hz AC, unstable or fluctuating power conditions, etc.
5.7.7 Metadata and Field Tools
5.7.7.1 Field recordings exist in relation to each other and to other events, objects and information.
Developments in the research communities are leading towards integrated data and metadata
acquisition tools which document and relate different objects and the times and place in which
they were created. Various international projects meanwhile have created tools that meet the
requirements of specific metadata schemes. Such tools offer a relatively complete metadata
collection and make transfer to established database systems easier and ensure accurate data
for future researchers. At the time of writing such tools and concepts are in an early stage of
development, they also tend to contain data that is discipline specific and so are not discussed here,
however, it is important that all the technical data described above is acquired for populating future
management and access systems. All data acquired should have in mind the transfer compatibility to
the final archiving system. Until standards come into being, use of UNICODE characters and XML
format is recommended.
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5.7.7.2 If metadata is collected manually, without using acquisition tools as mentioned above, it is
recommended to use a format that can easily be transferred to usual database structures.
Alternatively, institutes and archives sometimes provide their individual tools and if possible these
should be used in the field.
5.7.8 Time Factor
5.7.8.1 The time required to record an important event or interview can be quite extensive. The time
required to preserve a field recording can be reduced to the time it takes to ingest the data and
metadata if the field recording approach has been designed properly. If the system depends on
manual approaches it is quite likely that much valuable information will be lost due to human error,
or lack of resources to undertake this time consuming, but important, archival task.
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Chapter 6: Preservation Target Formats and Systems
6.1.1 Introduction
6.1.1.1 The following information on the management, long term storage and preservation of digitally
encoded audio is based on the premise that there is no ultimate, permanent storage media, nor
will there be in the foreseeable future. Instead, those managing digital audio archives must plan to
implement preservation management and storage systems which are designed to support processes
that go with the inevitable change in format, carrier or other technologies. The rate and direction of
technological change is something over which archives have no control and very little influence. The
aim and emphasis in digital preservation is to build sustainable systems rather than permanent carriers.
6.1.1.2 The choice of technological storage system is dependent on many factors, of which cost is but one.
Though the type of technology selected for preserving a collection may differ according to the
specific circumstances of the individual institution and its circumstances, the basic principles outlined
here apply to any approach to management and long term storage of digital audio.
6.1.2 Data or Audio Specific Storage
6.1.2.1 To effectively manage and maintain digital audio it is necessary to transform it to a standard
data format. Data formats are the file types, such as .wav, BWF, or AIFF, which computer systems
recognise. These files, unlike audio specific carriers, technologically define the limits of their own
content and are generally encoded in such a way that a loss of data is recognised and remedied by
the host system. IASA recommends the use of BWF as defined in Section 2.8 File Formats.
6.1.2.2 Audio specific recording formats which have been available in the past include DAT (Digital Audio
Tape) and CD-DA (Compact Disc-Digital Audio). DAT, though once largely used for the remote or
field recording of 16 bit, 48 kHz audio is now an obsolete recording system. IASA recommends that
any significant content recorded on DAT tape be transferred to a more reliable storage system in
accordance with the guidance provided in section 5.5 Reproduction of Digital Magnetic Carriers.
6.1.2.3 The recordable compact disc can be used to record audio in either audio-only (CD-A or CD-DA)
or data (CD-ROM) formats. In CD-DA format the encoded digital audio resembles an audio stream
and so does not have the advantages of a closed file such as might be recorded on the CD-ROM
formatted disc. In the latter though, less data can be stored on the same amount of disc space.
IASA does not recommend recording audio in CD-DA form as a preservation target format. There
are considerable risks associated with using a recordable CD as a target format in any form and
those risks are outlined in Chapter 8 Optical Disks: CD/DVD Recordable. The ever reducing prices
and increasing reliability of data management and storage systems make media specific storage
approaches, such as CD-R, unnecessary, or at least uneconomic.
6.1.3 Principals of Digital Preservation
6.1.3.1 Digital Mass Storage Systems (DMSS) Principles
6.1.3.2 The following information is based very closely on the practical aspects of Data Protection
Strategies from the UNESCO Guidelines for the Preservation of Digital Heritage. It is modified
only to reflect the possibility of systems that incorporate non-automated back up, and to reflect the
single format concerns of audio digital preservation. The section is included with the kind permission
of the author (Webb 2003:16.13).
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Preservation Target Formats and Systems
6.1.4 Practical Aspects of Data Protection Strategies
6.1.4.1 There is a reasonably standard suite of strategies used to manage data in long-term storage. Most
are predicated on an assumption that the data carrier itself does not need to be preserved, only the
data. The following comprises, in part, those strategies.
6.1.4.2 Allocation of responsibility: Someone must be given unambiguous responsibility for managing
data storage and protection. This is a technical responsibility requiring a particular set of skills
and knowledge as well as management expertise. For all collections, data storage and protection
require dedicated resources, an appropriate plan and must be accountable for these strategies, and
even very small collections must have access to the necessary expertise and a dedicated person
responsible for that task.
6.1.4.3 Appropriate technical infrastructure to do the job: Data must be stored and managed with
appropriate systems and on an appropriate carrier. There are digital asset management systems or
digital object storage systems available that meet the requirements of audio digital preservation
programmes, some approaches to which are discussed below. Once requirements have been
determined, they should be thoroughly discussed with potential suppliers. Different systems and
carriers are suited to different needs and those chosen for preservation programmes must be fit for
their purpose.
6.1.4.4 The overall system must have adequate capabilities including:
6.1.4.5 Sufficient storage capacity: Storage capacity can be built up over time, but the system must be able
to manage the amount of data expected to be stored within its life cycle.
6.1.4.6 As a fundamental capability, the system must be able to duplicate data as required without loss, and
transfer data to new or ‘refreshed’ carriers without loss.
6.1.4.7 Demonstrated reliability and technical support to deal with problems promptly.
6.1.4.8 The ability to map file names into a file-naming scheme suitable for its storage architecture. Storage
systems are based around named objects. Different systems use different architectures to organise
objects. This may impose constraints on how objects are named within storage; for example, disk
systems may impose a hierarchical directory structure on existing file names, different from those
that would be used on a tape system. The system must allow, or preferably carry out, a mapping of
system-imposed file names and existing identifiers.
6.1.4.9 The ability to manage redundant storage. As digital media has a small, but significant failure rate,
redundant copies of files at every stage are a necessity, especially the final storage phase.
6.1.4.10Error checking. A level of automated error checking is normal in most computer storage. Because
audio and audio-visual materials must be kept for long periods, often with very low human usage,
the system must be able to detect changes or loss of data and take appropriate action. At the very
least the strategies in place must alert collection managers to potential problems, with sufficient time
to allow appropriate action.
6.1.4.11Technical infrastructure must also include means of storing metadata and of reliably linking
metadata to stored digital objects. Large operations often find they need to set up digital object
management systems that are linked to, but separate from, their digital mass storage system, in order
to cope with the range of processes involved, and to allow metadata and work interfaces to be
changed without having to change the mass storage.
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6.1.5 Philosophy of System Sustainability
6.1.5.1 All technology, whether it be the hardware or software, formats or standards, will eventually change
as a result of market forces, performance requirements or other needs or expectations. The task of
the audio archivist charged with maintaining digital and digitised audio content is to navigate a way
through these technological changes such that the content of their collections are maintained for
current and future users in a reliable and authentic form in as cost effective way as can be managed.
6.1.6 Long Term Planning
6.1.6.1 Long term planning for a digital audio archive involves more than just the technical standards for a
data storage system. The technical issues must be carefully resolved, but the social and economic
aspects of running a digital storage system are vital to ensuring the continued access to the content.
Long term planning should consider the following issues.
6.1.6.2 The sustainability of the raw data: that is the retention of the byte-stream in its proper and
logical order. The data in the storage system must be returned to the system without change or
corruption. It is worth noting that computer systems expertise identifies a considerable risk in the
maintenance and refreshment of data, and only a well managed and designed approach to IT will
ensure adequate results.
6.1.6.3 Formats and ability to replay: Digital data is only useful in a sound archive if it can be rendered
as audio in the future. The proper choice of file format ensures that the future sound archive can
replay the content of the data files, or will be able to acquire the technology to migrate the files to
a new format. Not incorporating a lossy compression algorithm in that format allows that future
transformation process to occur without altering the original audio content.
6.1.6.4 Metadata, identification and long term access: All digital audio files must be identifiable and findable
in order for that audio material to be used and the value of the content realised.
6.1.6.5 Economics and Sound Archives: this includes the continued viable existence of the institutions that
support the data storage systems and repositories as well as those that own, manage, or gain value
from, the digital audio stored therein. The cost of maintaining a digital audio collection is ongoing and
their must be a plan and a budget that realistically plans for long term preservation of collections.
The cost of curating and managing the audio collections is also ongoing. Digital preservation is as
much an economic issue as a technical one. The requirements of ongoing sustainability demand at
their base a source of reliable funding, necessary to ensure that the constant, albeit potentially low
level, support for the sustainability of the digital content and its supporting repositories, technologies
and systems can be maintained for as long as it is required.
6.1.6.6 Storage, management and preservation alternatives: Given that the economic and technical
environment may well be volatile it is recommended that agreements be established between
archives and institutions regarding the storage of data as archives of last resort. This would require
some standard agreement about file formats and data organisation as well as social and technical
aspects of management of the content.
6.1.6.7 Tools, Software and long term planning: Hardware, software and systems are not things in
themselves to be preserved, but are merely tools to support the task of preserving the content. The
repository software D-Space, for example, does not describe itself as a preservation solution, but
only useful in “enabling institutions with a sustainable ability to retain information assets and offer
services upon them.” (DSpace, Michael J. Bass et al. 2002). The repository software itself is a tool,
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as are the various components designed to aid in operation, simplify processes, and automate and
validate the harvesting of metadata. Long term planning involves being able to change or upgrade
systems without endangering the content.
6.1.7 Defining the Digital Object
6.1.7.1 The audio file is only one part of the information that is to be preserved. The Reference Model for
an Open Archival Information System (OAIS) identifies four parts to the digital object, described
by them as the information package. These are the content information and the preservation
description information, which are packaged together with packaging information, and which is
discoverable by virtue of the descriptive information.
Content
information
Preservation
description
information
Packaging information
Package 1
Descriptive
information
about Package 1
Information Package Concepts and Relationships
6.1.7.2 Though the information may be distributed across the storage system, it is well to remember
that the conceptual package is the audio information, the ability to replay that audio, to know its
provenance and to describe and find it. There may also be critical relationships between the one
audio file and others in the collection, and these relationships are important to the use of the
material and so must also be preserved.
6.1.8 The Open Archival Information System (OAIS)
6.1.8.1 The Reference Model for an Open Archival Information System (OAIS) is a widely adopted conceptual
model for a digital repository and archival system. The OAIS reference model provides a common
language and conceptual framework that digital library and preservation specialists now share. The
framework has been adopted as an International Standard, ISO 14721:2003. Though some critics
identify shortcomings in the detail of the OAIS, the concept of constructing repository architectures in
a form that corresponds with the OAIS functional categories is critical to the development of modular
storage systems with interoperable exchange of content. The following sections of the Guidelines
adopt the major functional components of the OAIS reference model to assist in the analysis of the
available software and to develop recommendations for necessary development.
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6.1.8.2 There are a finite number of functions an archival digital repository must be able to perform in
order for it to reliably and sustainably perform the purpose for which it is designed. These are
defined in the Reference Model for an Open Archival Information System (OAIS) as Ingest, Access,
Administration, Data Management, Preservation Planning and Archival Storage.
Descriptive
info
Data
Management
Descriptive
info
Ingest
SIP
AIP
Archival
storage
Access
AIP
queries
result sets
orders
DIP
CONSUMER
PRODUCER
Preservation planning
Administration
MANAGEMENT
6.1.8.3 The OAIS also defines the structure of the various information packages that are necessary for the
management of the data, according to the place in the digital life cycle. These are the Submission
Information Package (SIP), Dissemination Information Package (DIP) and Archival Information
Package (AIP). A package is the conceptual parcel of the data and relevant metadata and descriptive
information necessary to the particular object. This object is conceptual only in the sense that the
package contents may be dispersed in the system or collapsed into a single digital object. OAIS
defines an information package as the Content Information and associated Preservation Description
Information which is needed to aid in the preservation of the Content Information.
6.1.8.4 The SIP is an Information Package that is delivered to the system for ingest. It contains the data to
be stored and all the necessary related metadata about object. The SIP is accepted into the system
and used to create an AIP.
6.1.8.5 The AIP is an Information Package which is stored and preserved within the system. It is the
information package the system stores, preserves and sustains.
6.1.8.6 The DIP is the information package created to distribute the digital content. There are three roles in
this system. First is access, and this DIP would be in a form that the users can use and understand.
Second is exchange for the purpose of distributing risk. An archival repository may choose to share
parts of its content with other similar institutions, or with an organisation whose role is archival
storage. In this case the DIP would contain all the relevant metadata necessary to undertake this
role. The third is for distributing content to archives as a last resort. The scenario where a particular
archive or institution no longer has the resources to maintain its collection is not difficult to imagine.
A standard DIP for this purpose allows other similarly architected systems to undertake the role
with the minimum of manual intervention.
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6.1.9 Trusted Digital Repositories (TDR) and Institutional Responsibility
6.1.9.1 The technical specification of the digital storage environment is an important part of ensuring
that the digital content that is managed is still accessible to researchers in the future. It is not of its
own, however, enough to ensure that this will be achieved. The institution within which the digital
archive resides has to be able to ensure that the content it manages is curated and maintained
responsibly. In 2002 the Research Libraries Group (RLG) and the Online Computer Library Center
(OCLC) jointly published “Trusted Digital Repositories: Attributes and Responsibilities” (TDR), which
articulated a framework of attributes and responsibilities for trusted, reliable, sustainable digital
repositories which were “required for an archive to provide permanent or indefinite long-term
preservation of digital information”.
6.1.9.2 These attributes include compliance with the OAIS reference model, organisational viability, financial
sustainability, technological and procedural suitability, the security of the system and the existence of
appropriate policies to ensure that the steps are taken to manage and preserve the data.
6.1.9.3 The practical instantiation of this is a document known as the “Trustworthy Repositories Audit and
Certification (TRAC): Criteria and Checklist” (2007). Using this document an archival institution
can establish whether the practices, approaches and technologies they have or are planning to
implement are appropriate to the permanent preservation of the digital information for which they
have responsibility.
6.1.9.4 The concern which the checklist addresses incorporates three main areas: organisational
infrastructure; digital object management and technologies; and technical infrastructure and security.
6.1.9.5 Organisational infrastructure provides a series of checks against appropriate governance and
organisational viability, organisational structure and staffing, procedural accountability and policy
framework, financial sustainability and a consideration of the licenses, and liabilities. Digital object
management section considers the acquisition of content, the creation of an archivable package,
planning for preservation, archival storage and planning, information management and access control.
The third part of this checklist audits the system infrastructure, the use of technologies appropriate
to the tasks and system and institution security.
6.1.9.6 The terminology used in the “Trustworthy Repositories Audit & Certification (TRAC): Criteria and
Checklist” is chosen to represent digital archives in the broadest sense of the word, and so the
document’s meaning may occasionally appear opaque to an audio archivist. Nonetheless, the issues
examined and tested by it are critical to the planning and management of a digital audio archive. It
is strongly recommended that the digital sound archivist uses the checklist to examine the suitability
of an institution to manage a digital collection, or to identify weaknesses within an existing digital
preservation strategy.
6.1.10 Audio Archives and Technical Responsibility
6.1.10.1 Though a particular institution may be responsible for the management of a collection or set of audio
items, it does not necessarily follow that institution will undertake the responsibility for maintaining the
digital storage system. An institution may instead become a part of a distributed storage system, or may
identify a third party provider to archive their content in a more standard approach.
6.1.10.2A distributed data storage approach such as that being promoted and developed for web based
material by Stanford University under the name of LOCKSS (Lots of Copies Keep Stuff Safe)
replicates data in a number of places on the web. The system manages the data on the grid and risk
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of loss of data is reduced because the information can be found in many different places. Such a
system is not appropriate for material which has access restrictions or copyright which prohibits
dissemination. Such a system also requires that a development and management responsibility to be
shouldered by an institution.
6.1.10.3An institution may decide that they do not have the technical capability to undertake the
development and management of a digital storage system. In this case they may establish a
relationship with a third party provider. That provider may be another archive which will take the
collection and store its content, or may be a commercial provider who will provide and manage the
storage and content for a fee.
6.1.10.4 The information provided here is provided as though the institution is intending to take on its own
preservation. However, if any of the above alternatives are considered, then this information is useful
for determining if those approaches are reliable and valid.
6.1.11 Digital Repository Software, Data Management, and Preservation Systems:
6.1.11.1Digital repository software is generally that software which supports storage and access to the
digital content. It should incorporate indexing and metadata systems that manage information about
the content, and a variety of tools to find and report on the content.
6.1.11.2Data management is the management of the byte stream, or data, that the system is responsible for.
This may include back up procedures, multiple copies and changes.
6.1.11.3Preservation processes are those that ensure the content remain accessible in the long term, that
the content is still meaningful and that the data management system’s tasks are documented and
maintained. All three of these steps are necessary to achieve long term preservation to content.
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6.2 Ingest
6.2.1 Submission Information Package (SIP)
6.2.1.1 The SIP is an Information Package that is delivered to the repository and digital storage system for
ingest. The SIP includes the audio data to be stored and all the necessary related metadata about
the object and its content. Ingest, in the OAIS model, is the process that accepts the content and
all its related metadata (SIP), verifies the file, extracts the relevant data and prepares the AIP for
storage, and ensures that AIPs and their supporting Descriptive Information become established
within the OAIS.
6.2.1.2 A digital repository and preservation system should be able to accept and validate an audio file.
Validation is a process that ensures that the files which are being accepted into the digital storage
system comply with the standards. Non standard files may become difficult to use in the future
when current replay systems no longer exist. Tools exist for automated validation of file formats,
and some open source solutions, like JHOVE (JSTOR/Harvard Object Validation Environment), are
available and being further developed.
6.2.2 Format
6.2.2.1 IASA recommends the use of .wav or preferably BWF .wav files [EBU tech 3285]. The difference
between the two is that the BWF contains a set of headers which can be used to organise and
manage metadata. Though BWF metadata is adequate for many purposes, in some sophisticated
systems and exchange situations a more comprehensive package is required, and in these
circumstances Metadata Encoding and Transmission Standard (METS) is often used. The METS
schema is a standard for encoding descriptive, administrative, and structural metadata regarding
objects within a digital library, expressed using XML (eXtensible Markup Language). A METS
package, which consists of metadata and content, is often used as an exchange standard between
digital archives.
6.2.2.2 Material eXchange Format (MXF) is a container format for professional digital video and audio
media defined by a set of SMPTE standards. MXF has been mostly taken up by the video archiving
community, though it is capable of managing audio. Like METS, it is primarily a set of metadata which
“wraps” the content, in this case, audio. Both these are very useful formats in the exchange and
management of content and information between archives and repositories.
6.2.2.3 The format of the SIP will depend on the system and the size and sophistication of the enterprise.
It is quite possible to establish a viable archive using .wav files and manually entering most of the
necessary metadata into the system by hand, and acquiring the necessary technical metadata at
the ingest stage. This however, would only be appropriate for the smallest of collections. Large
collections with remote and separate digitisation processes and large quantities of material must
build sophisticated ingest and data exchange systems to ensure the content is adequately ingested
into the data storage systems. Production and verification software generates much of this data
as standardised XML-files that may be used for preservation purposes. The National Library of
New Zealand Metadata Extractor tool, for example, is a Java-based tool that extracts preservation
metadata from digital objects and outputs that metadata in a standard format (XML).
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6.2.3 Preservation Metadata
6.2.3.1 The metadata needed to manage preservation processes at the ingest stage is all the information
regarding the creation of the digital audio object and the changes to format that have occurred prior
to ingest. In this way the technical provenance of the object is preserved, which allows a pathway
between the present form of the item and original from which it was created to be traced.
6.2.3.2 BWF has a non-compulsory recommendation for BWF entitled “Format for CodingHistory field
in Broadcast Wave Format” http://www.ebu.ch/CMSimages/en/tec_text_r98–1999_tcm6-4709.pdf
which describes how changes to the file may be described. Local usage of the ASCII free text field
allows the description of the technical equipment or software that was used in the creation of the
digital audio object.
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6.3 Archival Storage
6.3.1 Archival Information Package (AIP)
6.3.1.1 The definition of the term Archival Storage in OAIS includes the services and functions necessary for
the storage of the Archival Information Package (AIP). Archival storage encompasses data management
and includes processes such as storage media selection, transfer of AIP to storage system, data security
and validity, backup and data restoration, and reproduction of AIP to new media.
6.3.1.2 AIP, as defined in OAIS reference model (CCSDS 650.0-B-1 Reference Model for an Open Archival
Information System (OAIS)), is an information package that is used to transmit archival objects into a
digital archival system, store the objects within the system, and transmit objects from the system. An
AIP contains both metadata that describes the structure and content of an archived essence and the
actual essence itself. It consists of multiple data files that hold either a logically or physically packaged
entity. The implementation of AIP can vary from archive to another archive; it specifies, however, a
container that contains all the necessary information to allow long term preservation and access to
archival holdings. The metadata model of OAIS is based on METS specifications.
6.3.1.3 From physical point of view the AIP contains three parts; metadata, essence and packaging information,
which all consists of one or more files (see 6.1.3 Defining the Digital Object). Packaging information
can be thought as wrapper information and it encapsulates metadata and essence components.
6.3.2 Archival Storage basics
6.3.2.1 Archival Storage provides the means to store, preserve and provide access to archived content.
In small systems the storage can stand alone and may be manually operated, but in larger systems
storage is usually implemented in conjunction with cataloguing applications, asset management
systems, information retrieval systems and access control systems in order to control and manage
archived content and provide a controlled way to access them.
6.3.2.2 Archival Storage must be connected to equipment that ingests and creates the digital asset to be
archived, and it must provide a secure and reliable interface that can be used to import assets to the
storage system.
6.3.2.3 A system that is used to store archival content must be reliable in several ways: It must be available
for use without any significant interruptions, and it must be able to report to the system or user
who imports content whether the import was successful or not, thus enabling the importing party
to delete the ingest copy of the of the archival file if appropriate. Archival Storage must also be able
to preserve the content it manages for a long period of time and be able to protect the content
from all kinds of failures and disasters.
6.3.2.4 An Archival Storage system should be built according to the needs of its functional owner: it must
be correctly-sized to carry out the tasks that are needed, and manage the capacities that are
required in every day operations. In addition, Archival Storage must provide controlled access to the
content it manages for the users who have permissions or rights to access the content.
6.3.3 Digital Mass Storage Systems (DMSS)
6.3.3.1 A Digital Mass Storage System refers to an IT based system that has been planned and built to be able
to store and maintain large amounts of data for a given or extended period of time. These systems
come in many forms; a basic DMSS could be a personal computer which has large enough hard disk
drive and some kind of catalogue that can be used to keep track of the assets the system possesses.
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A more complex DMSS may consist of hard disk drive and/or tape storage and group of computers
that control the storage entity. A DMSS can also contain many tiers of storage with different
characteristics; a fast Fibre Channel based hard disk drive tier can be used to cache assets whose
access time is critical while a tier built of cheaper hard disk drives could be used to hold material
whose access time is not so critical, and finally tape based storage can be used as the most costeffective tier of storage.
6.3.3.2 When a number of different storage technologies are used in a large system to build the functional
entity, a HSM (Hierarchical Storage Management) system is usually deployed in such a way that it
supports the different technologies working together. Larger scale systems may also be distributed
geographically in order to achieve better performance and make the system more fault tolerant.
6.3.4 Data Tape Types and Formats Introduction
6.3.4.1 The following is an outline of some of the main data tape formats and tape automation systems that
may be used for storing AV content in data form. Data tapes are only used in conjunction with other
components of a DMSS. It is prudent to commence a section on comparison of the various data tape
formats with a reminder that no carrier is permanent and that, all things being equal, they will only be
viable as long as the data systems in which they are incorporated continue to support them.
6.3.5 Data Tape Performance
6.3.5.1 Format geometry and dimensions govern performance. Data transfer speed, one aspect of
performance, is a direct product of the number of tracks written and read simultaneously, as well
as the tape-head speed, linear density and the channel-code. Similarly, physically smaller, lighter tape
housings are faster to move in a robotic library. Data density is a product of:
6.3.5.1.1 tape length and thickness trade-offs
6.3.5.1.2 track width and pitch
6.3.5.1.3linear density of data payload within each track
6.3.6 Tape Coatings
6.3.6.1 There are two main types of tape coatings: particulate and evaporated. The earliest coated data
tapes used metal oxides similar to video tape, whereas more recent data tapes use metal particles
(MP). Pure iron with inert ceramic and oxide passivation layers is dispersed in polymer binders
which are applied evenly to a PET or PEN base-film or substrate which in turn provides dimensional
stability and strength under tension. Some of the highest density data tapes currently on the market
now use evaporated metal foil coatings of cobalt alloys and similar material to those used on hard
disks. This achieves a much higher purity of magnetic material and allows thinner coatings. Most
metal-evaporated (ME) tapes have a protective polymer coating similar to the binder material on
MP tapes. The more recent formulations include a ceramic protective layer as well. Several of the
early ME tapes failed during heavy usage due to de-lamination (Osaki 1993:11).
6.3.7 Tape Housing Design
6.3.7.1 Two basic styles of housings are used, dual-hub cassettes, which may enable faster access times and
single-hub cartridges, which offer greater capacity within a given external volume.
6.3.7.2 Dual hub cassettes include:
3.81mm, principally DDS [derived from DAT]
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QIC [quarter-inch cartridge] and Travan
8mm formats, including Exabyte and AIT
DTF
Storagetek 9840
6.3.7.3
Single-hub cartridges include:
IBM MTC and Magstar formats such as 3590, 3592 and TS1120
Quantum S-DLT and DLT-S4
LTO Ultrium [100, 200, 400 & 800 GB]
Storagetek 9940 and T10000
Sony S-AIT
6.3.7.4 Neither design is necessarily superior for long-term archiving, since the life is governed by a range of
details specific to each format. For instance, some models of the single-ended ½-inch cartridges have
large-diameter guides within the housing, which ensure minimum friction and accurate tape guidance.
Problems have been experienced with the leader latching mechanism on older single-ended cartridges,
although more recent designs have improved reliability in this area. Some dual-hub cassettes can be
positioned to park halfway along the tape to minimise the amount of spooling time to any particular
file. This contradicts the traditional practice in AV archives of spooling tapes carefully to one end
before storage so that only leader tape is exposed to the threading mechanism. Tapes generally don’t
incorporate a hermetically sealed enclosure in the way that hard disks are protected.
6.3.8 Linearly and Helically Scanned Tapes
6.3.8.1 Data tapes may be written or read with a fixed head, generally described as linear, or with a rotating
or helical head. Linear tapes typically follow a serpentine track layout, and it has been argued
that this shuttling can lead to wear or a so-called shoe-shine effect. In practice, modern tapes are
designed to last for large numbers of passes, however, it is still prudent to access frequently used
content from hard disc. Tapes, which experience chemical decomposition from hydrolysis and other
causes, will usually run better over fixed guides and components in the tape path at speeds of
around1-2 m/s or greater, which are typical of fixed-head or linear formats. Rotary-head or helical
formats typically have higher tape-head speeds which create a greater air-bearing effect between the
tape surface and the read-write heads, but the linear tape speed over the fixed guides and heads is
much slower, so this is where fouling often occurs.
6.3.9 Ancillary Storage and Access Devices
6.3.9.1 Formats such as AIT include solid-state ‘Memory in Cassette’ or MIC which stores file positional
information similar to a Table of Contents (TOC) on Compact Disks for rapid location of data. DTF
uses rf memory.
6.3.10 Format Obsolescence and Technology Cycles
6.3.10.1 The inherent nature of data storage is of constant progress and development, which means inevitable
change, and ongoing obsolescence. Realistic long-term management of content must accept and build
upon the continuing evolution and upgrading of hardware and media. Although central infrastructure
such as data cabling or storage libraries may remain in operation for ten or twenty years, individual
tape drives and media have a finite life much shorter than this. All of the main data tape formats have
development roadmaps projecting upgrades every 18 months to 2 years. Backward compatibility for
read-only access is sometimes assured over one or two generations of media within any common
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family. As a result, each generation of tape drives and media may be viable for 4 to 6 years, after
which time it is essential to migrate the data and move on.1 Also the hardware maintenance cost of
mass storage systems tend to rise notably when the system gets older than its projected life or the
guarantee period ends. After this it may be difficult to obtain new spare parts for the tape libraries or
tape drives, for example. A summary of projected roadmaps is presented below. Many formats have
read-only compatibility with at least one previous generation.
Family
Quantum
SDLT
IBM
Sun Storagetek
LTO
1st
2nd
3rd
Generation
Generation Generation
SDLT220
SDLT320
SDLT600
110GBytes
160GBytes
300GBytes
3592 2004
300GB
40MB/s
9940B 2002 T10000 2006
200GB
500GB
30MB/s
120MB/s
LTO-1 2001 LTO-2 2003 LTO-3 2004
400GB
100GB
200GB
80MB/s
20MB/s
40MB/s
Sony S-AIT S-AIT 2003
500 GB
30MB/s
Sony AIT
S-AIT2 2006
800 GB
45MB/s
AIT-3 2003
100 GB
12MB/s
4th
5th
6th
Generation
Generation Generation
DLT-S4
800GBytes
TS1120 2006 700GB 104MB/s
T10000B-2008 ITB
120MB/s
LTO-4 2007
LTO-5 no
800GB 120MB/s date (2009+)
1.6TB
180MB/s
(estimated)
AIT-4 2005
200 GB 24MB/s
LTO-6 no date
(2011+)
3.2TB
270MB/s
(estimated)
Table 1 Section 6.3: Projected Development Roadmap for Data Tapes
6.3.11 Automated Robotics or Manual Retrieval
6.3.11.1 For small-scale operations it is possible to back up data from a single workstation onto a single data
tape drive and manually load tapes for storage on traditional shelving, and even small scale networked
systems will undertake manual backup of their storage (see also Chapter 7 Small Scale Approaches
to Digital Storage Systems). The same guidelines for storage environments apply as for other magnetic
tapes, though increased attention to minimising the presence of dust and other particulates and
pollutants would be beneficial. For larger-scale operations, particularly in countries where labour costs
are high, and capital equipment budgets are favourable, a degree of automation is normally desirable
and more economical than purely manual systems. The degree of automation depends upon the scale
and consistency of the task, type of access to the content, and the relative costs of the main resources.
6.3.11.2Autoloaders and Robotic Tape Libraries: The next step from single drives is the small-scale autoloader, which usually has one drive (occasionally two), and a single row or carousel of data tapes
which are fed in sequentially to support backup operations. One of the key differences between
autoloaders, and large-scale robotic libraries is that the recorded tapes are not logged by the backup
software in a central database which can then enable automated retrieval. The task of searching,
1
This implies a degree of waste and environmental pressure beyond the scope of our purely technological discussion, but in reality, a
large-scale library of older data tapes will consume more polymers and require more petrochemicals for manufacture than a newer,
high-density system with more energy-efficient drives and robotics, occupying less real-estate at the same time.
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retrieving and reloading individual files still falls to a human operator. All that autoloaders do, as the
name implies, is to allow a series of tapes to be written or read sequentially to overcome the size
limitations of individual data media, and to negate the requirement for a human operator’s presence
to load the next tape in a long backup sequence.
6.3.11.3By way of contrast, even the smallest robotic tape libraries are programmed to behave as a single,
self-contained storage system. The location of individual files on different tapes is transparent to the
user, and the library controller keeps track of addresses of files on each tape, and of the physical
location of tapes within the library. If tapes are removed or reloaded, the robotic sub-system rescans the tape slots as it initialises, to update its inventory with metadata from barcodes, rf tags, or
memory chips in the tape housings.
6.3.11.4Large tape libraries have some benefits when compared to the smaller tape libraries. They can be
built to be redundant and distributed, i.e. downtime can be minimised and the read/write load can
be balanced between several similar systems. Large tape library can also be used as a multi-purpose
system; they can, for example, maintain a company’s normal IT backups as well as manage all
archived video and audio.
6.3.11.5Data tapes or cartridges used in a robotic system will have some system of barcoding, rf tags or
other ID. These optical or electromagnetic recognition systems sometimes operate in conjunction
with MIC for supplementing information about tape ID and content. Some formats have a global ID
system for barcoding tapes so that a tape used in one robotic library can be recognised in another
library system.
6.3.11.6 Backup and Migration Software and Schedules: Some confusion and misunderstanding exists both
in IT circles, and in the wider community as to the purpose and operation of long-term data archives.
There are two popular misconceptions regarding long term data archives. The first; that archiving is
the process of moving infrequently used material from expensive, on-line networked disc storage, to
less expensive, inaccessible offline shelving from whence it may never be retrieved and the other; that
backup is a regular daily and weekly routine of making a copy of everything stored in the system.
6.3.11.7With regard to the first misconception, the reality is that some of the most important and valuable
material may not be used for months or years, but its survival must be guaranteed unequivocally.
Likewise with the second, if suitable rules are established, vast amounts of material may not need to
be replicated daily or weekly when only small percentages are updated. In practice, while a stringent
regime of replicating data on different media in different locations is essential to minimise risks from
technology failures and to ensure recovery from disasters, the particular characteristics of digital
heritage material requires some procedures that differ from routine IT data management.
6.3.11.8Conventional HSM (Hierarchical Storage Management) systems may be optimised for backing up
everything on a regular basis, and moving out infrequently-used content to inaccessible locations, but
the better systems can be configured to suit the business rules and practices in archives of different
sizes with different levels of access. A medium-sized organisation may ingest 100 GB of audio data
every week or 1TB of video. It is fairly straightforward to ensure that copies are made as soon as
valuable material is ingested, and that frequently used material remains accessible.
6.3.11.9 Some of the primary tasks of storage management software are to optimise the use of resources
and to manage devices in the hardware layer, while regulating traffic with minimal delays to users.
HSM software offers a choice of conditions for migrating files from on-line disk to tape, such as
older than a certain date, larger than a nominated size, located in particular sub-folders or when
available disk space falls outside certain limits (high and low watermark).
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6.3.11.10Typically, where both high resolution files, as well as low resolution access copies are produced, the
larger, high resolution files used for preservation and broadcast will be migrated to tape to free
up space on the more expensive hard disk array. A balance is needed to maintain availability of
material, and to optimise use of tape drives and media. If tapes are being accessed very frequently,
a large number of mounts and unmounts, spooling and restore operations will degrade system
performance. More sophisticated content management systems sometimes incorporate lower levels
of storage management so that users are less aware of individual files and components that support
the system.
6.3.12 Selection and Monitoring of Data Tape Media
6.3.12.1As with any conventional preservation system, it is important not only to have backups and
redundancy in case of failures in media or components, but it is vital to establish and to measure
performance standards for key parts of the system. Software such as SCSI-Tools will allow a lower
level of interrogation of individual drives and devices on a network to determine if media and
hardware are performing at their optimum level. LTO tape has an interface for data monitoring,
however this functionality is rarely utilised though it would be advantageous for archival systems.
Some HSM systems are capable of monitoring the quality of stored assets on a regular basis. These
systems monitor the error rates of tapes while users access the assets or read the assets without
user intervention if a tape has not been used during a certain period of time.
6.3.13 Costs
6.3.13.1Typically, the cost of data tape storage is spread in four areas: Tape media: procurement and
replacement of primary and backup tape media every 3–5 years. Tape drives: procurement and
replacement every 1–5 years, with support. Robotic Library purchase and maintenance within a
10 year life-cycle, and software purchase, integration/development and maintenance.
6.3.13.2In a manual system, the costs for shelving will be lower, although the space requirement for staff
is greater, and the labour cost for manual retrieval and checking is higher. In an automated robotic
system, much of the human cost is offset by up-front expense for hardware and software. Large
scale robotic tape libraries can be purchased in a modular fashion to spread the cost over several
years as demand for storage grows. Within the life of a robotic tape library, individual components
such as tape drives will be replaced by newer technology every three to five years. If content from
an archive is accessed continuously the life time of drives can be considerably short, even only one
year or less. Older tape media and drives may be kept on hand for redundancy if required. If an
archive does not grow rapidly, the present and next generation of tapes and drives can co-exist in
a tape library while the archive content is migrated to the next generation of media or technology.
If an archive grows continuously it may be cost-effective to create a tape library of a specific size
to only store the amount of content that shall be archived during the life time of the then current
technology, and to then acquire a new larger tape library to store the content that shall be stored
using the next generation of technology including the old content that will be migrated. The later
approach is also necessary if old and new technology cannot co-exist in the same unit.
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6.3.13.3It is good business practice to keep at least one redundant copy of data off-site or geographically
separate. Typically a radius of 20 to 50 km is common for natural and man-made disasters, and still
allows manual retrieval within a few hours. To reduce risks further, redundant copies should be on
different batches or sources of media, or even on different technologies. Some data tapes are only
manufactured at a single supplier, and chances of a single point of failure are increased. Three copies
of data are safer than two, and although costs for media increase, the hardware and software costs
are only slightly higher than for the first copy.
6.3.14 Hard Disk Drives (HDD) Introduction
6.3.14.1Hard Disk Drives (HDDs) have served as the primary memory and data storage in computers since
IBM introduced the model 3340 disk drive in 1973. Nicknamed “the Winchester”, because it had
30MB of fixed memory and 30MB of removable and the working designation of 30/30 resembled,
in name at least, the famous rifle, it pioneered head designs that made operation of the hard disk
viable. Subsequent reduction in size and more recent developments in head and disk design have
greatly increased the reliability of disk drives, leading to the robust designs in common use today.
6.3.14.2Data managers whose responsibility it is to maintain data have considered the hard disk too
unreliable to use as the sole copy of an item, and too expensive to use in multiple, and consequently
more reliable, disk arrays. The data on HDDs has consequently been duplicated on multiple tape
copies to ensure its survival. As stated above (6.1.4 Practical Aspects of Data Protection Strategies
and 7.6 Archival Storage) all data systems must have multiple and separate copies of all data. While
experts tend to agree that the most reliable data system consists of a HDD array supported by
multiple duplicates on tape, the continued reduction in costs and improvement in reliability make the
concept of identical duplicates of data on separate hard disks a possibility. The principle of multiple
media remains, however, and disk only storage constitutes a risk.
6.3.15 Reliability
6.3.15.1Loss of data as a consequence of disk failure and head crashes has made most data professionals
suspicious of HDDs, however manufacturers now claim annualised failure rates of less than one
percent and an operational life of 40,000 hours (Plend 2003). High reliability drives may have an
even longer operational life, termed by manufacturers as “mean time between failure”. Though
HDDs are self-contained and sealed and so protected from damage, most failures in disk drives
occur in two opposing ways: as a result of wear through extended use, or as power to the drive is
turned on or off. The dilemma is whether to leave the disk on, and increase wear, or turn it on and
off and increase risk of failure.
6.3.16 System Description, Complexity and Cost
6.3.16.1As noted in Section 2, Key Digital Principles, the more recent generations of computers have
sufficient power to manipulate large audio files. All recent generation computers incorporate hard
disks of adequate speed and size, and an external HDD adapter can be plugged into a USB, Firewire
or SCSI port. The system complexity and the degree of expertise required to run such systems is
not much greater than is necessary for desktop computer operation.
6.3.16.2When large quantities of audio and audiovisual material required for access are stored on HDDs,
the disks are usually incorporated into a RAID (Redundant Array of Inexpensive (or Independent)
Disks). RAID increases the reliability of the hard disk system, and the overall access speed by treating
the array of disks as one large hard disk. If a disk fails, it can be replaced and all the data on that disk
can be reconstructed with data from the rest of the disks in the array. The level of failure the system
105
13
63
125
250
625
1250
2500
Recommended
# of tape drives
2
4
8
12
18
36
72
Maximum #
of drives
4
16
16
16
56
88
176
106
HW maintenance,
year 1 (€)
2.420
3.454
11.808
15.787
27.380
47.542
99.272
SW maintenance,
year 1 (€)
n/a
n/a
490
582
1.068
2.115
4.221
HW maintenance,
year 2 (€)
2.420
4.958
13.817
19.323
34.111
66.734
99.272
SW maintenance,
year 2 (€)
n/a
n/a
490
582
1.068
2.115
4.221
2.420
4.958
13.817
19.323
34.111
66.734
99.272
HW maintenance,
year 3 (€)
n/a
n/a
490
582
1.068
2.115
4.221
2.514
4.958
13.817
19.323
34.111
66.734
99.272
n/a
n/a
490
582
1.068
2.115
4.221
Notes to the tables:
• Prices are averages of list prices from multiple vendors. A price that a customer has to pay is usually somewhat lower.
• Prices indicate price of raw capacity. At least double amount of tape media will be needed for backup purposes.
• Price in the system price column includes cost of tapes and drives for the capacity in question, but does not include any HSM software or hardware
• The tables indicate only investment costs and maintenance fees that have to be paid to a vendor. In addition to this, also costs from electricity, cooling,
machine room, management, etc. must be included in individual calculations. Electricity and cooling of tape library system might cost 10% of purchase price
over five year period.
n/a
n/a
490
582
1.068
2.115
4.221
2.514
4.958
13.817
19.323
34.111
66.734
99.272
Cost per
GB (€)
2,05
1,14
1,34
1,03
0,89
0,86
0,84
System Tape price
Drive
price (€)
(€)
price (€)
20.480
97
7.625
56.800
97
10.175
134.050
97
12.725
205.350
97
12.725
446.938
97
15.975
864.517
97
15.975
1.687.690
97
15.975
Table 3 Section 6.3: Yearly Maintenance Costs of LTO-4 technology based Storage Systems
10 TB
50 TB
100 TB
200 TB
500 TB
1000 TB
2000 TB
Capacity
SW maintenance,
year 3 (€)
Table 2 Section 6.3: Investment Costs of LTO-4 technology based Storage Systems
10 TB
50 TB
100 TB
200 TB
500 TB
1000 TB
2000 TB
# of tapes
HW maintenance,
year 5 (€)
HW maintenance,
year 4 (€)
Native tape
capacity (GB)
800
800
800
800
800
800
800
SW maintenance,
year 5 (€)
SW maintenance,
year 4 (€)
Capacity
will tolerate, and the speed of recovery from such failures is a product of the RAID levels. RAID is
not designed as a data preservation tool, but as a means of maintaining access through inevitable
disk failures. The appropriate RAID level for any particular installation, and the requirement for
duplication of controllers, is dependant on the particular circumstance and the frequency of data
duplication. A RAID requires that all disks in the array be turned on when any part of the disk is
in use. All RAIDs containing archival material, as with all digital data, must be duplicated more than
once on other carriers.
5–10
10–14
50
100
200
500
1000
2000
107
826
HW maintenance,
year 1 (€)
1.206
5.822
10.514
21.724
57.061
130.203
223.778
750
SW maintenance,
year 1 (€)
1.125
6.125
8.500
12.750
37.250
66.250
124.250
1.206
5.822
10.514
21.724
57.061
130.203
223.778
826
HW maintenance,
year 2 (€)
750
1.125
6.125
8.500
12.750
37.250
66.250
124.250
826
1.206
5.822
10.514
21.724
130.394
263.537
477.121
Drive
price (€)
1.000
1.000
1.800
1.800
1.800
1.900
1.900
1.900
750
1.125
6.125
8.500
12.750
37.250
66.250
124.250
2.600
12.365
22.391
44.956
130.394
263.537
477.121
1.845
Cost per
GB (€)
2,38
2,00
2,49
2,31
2,28
2,41
2,57
2,39
750
1.125
6.125
8.500
12.750
37.250
66.250
124.250
HW maintenance,
year 5 (€)
2.600
12.365
22.391
44.956
130.394
263.537
477.121
1.845
1.125
6.125
8.500
12.750
37.250
66.250
124.250
750
SW maintenance,
year 5 (€)
• Prices are averages of list prices from multiple vendors. A price that a customer has to pay is usually somewhat lower.
• Price in the system price column includes cost of hard disk drives for the capacity in question.
• The tables indicate only investment costs and maintenance fees that have to be paid to a vendor. In addition to this also costs from electricity, cooling, machine room, management, etc.
must be included in individual calculations. Electricity and cooling of hard disk drive system might cost 30% to 40% of purchase price over five years period.
Notes to the tables:
Table 5 Section 6.3: Yearly Maintenance Costs of HDD Based Storage Systems
10 TB
50 TB
100 TB
200 TB
500 TB
1000 TB
2000 TB
5 TB
Capacity
SW maintenance,
year 2 (€)
Table 4 Section 6.3: Investment Costs of HDD Based Storage Systems
5 TB
10 TB
50 TB
100 TB
200 TB
500 TB
1000 TB
2000 TB
System
price (€)
11.884
19.997
124.334
230.914
456.942
1.202.726
2.566.513
4.782.584
HW maintenance,
year 3 (€)
# of drives
SW maintenance,
year 3 (€)
Size of drive
(GB)
500–1000
750–1000
1000
1000
1000
1000
1000
1000
HW maintenance,
year 4 (€)
Drive
technology
SATA
SATA
SATA/FATA
SATA/FATA
SATA/FATA
SATA/FATA
SATA/FATA
SATA/FATA
SW maintenance,
year 4 (€)
Capacity
6.3.17 Disk Only Storage
6.3.17.1RAID arrays are scalable within the limits of the system, however individual HDDs are infinitely
scalable by simply adding more drives. Since the introduction of the IBM 3340 HDD, storage
capacity has increased rapidly, almost exponentially, while costs have fallen. These changes, linked
with an improvement in reliability, have led some to suggest that HDDs could be used as both
the primary storage system and the back up copy. There are three difficulties associated with this
approach: Firstly, hard disk life is estimated in terms of usage-time, that is the number of hours of
operation. There has been no testing of the life of an infrequently used HDD. Secondly, having data
on different types of media is advantageous as it spreads the risk of failure. Therefore the approach
should be considered very cautiously. Finally, there is no way of monitoring the condition of the
hard disk on the shelf without turning it on at regular intervals and thereby compromising the
advantage gained by having the disk turned off (see section 6.3.18 below, Monitoring of Hard Disk
Media). Multiple carriers (eg Tape and Hard disk) remain the preferred option. Hard disks should be
implemented within an integrated system.
6.3.18 Hard Disk Storage Systems
6.3.18.1Hard Disk Storage Systems are centralised systems that are used to maximise disk storage utilisation
and to provide large capacities and/or high performance. These systems are used in conjunction
with server computers so that server have only small amount of internal hard disk storage or do
not have it at all. These kind of systems are often used in mid and large size environments as storage
for an archiving system. Alternatively an archiving system can share a centralised storage system
with a number of other computer systems. The size of a system can vary from 1 terabyte to several
petabytes. It should be taken into consideration that performance characteristics of a storage system
can vary notably according to its chosen configuration and it is essential that the actual needs for a
system are carefully planned beforehand and a qualified professional is used to configure the storage
structure and interfaces of a system to produce the best value for ones investment.
6.3.18.2Centralised disk storage systems are designed to provide better error resilience than independent
hard disk drives. These systems provide several alternative levels of RAID protection, their
components can be redundant in order to avoid single point of failures, and systems can be locally
or geographically distributed to protect valuable assets from different kind of failures and disasters.
6.3.18.3The connection between the storage system and the computers it serves play important role
regarding performance of a system. Generally speaking, two methods used are NAS (Network
Attached Storage) and SAN (Storage Area Network). While NAS utilises regular IT network like
Ethernet to move data between computer and storage system SAN uses switched Fibre Channel
connections. NAS systems can operate at 100 Mbit/s, 1 Gbit/s and 10 Gbit/s speeds while SANs
operate at 2 Gbit/s or 4 Gbit/s. Both technologies have clear road map to the future and their
performance can be expected to grow in the future. SAN technology is usually chosen for more
demanding environments since it gives better performance due to specific design. For example, the
in/out (I/O) block size can be controlled more effectively in SAN environments while networking
protocols tend to force NAS systems to use quite small I/O blocks. From economical point of view
NAS technology is cheaper than SAN technology.
6.3.19 HDD Life
6.3.19.1As stated above, a life of 40,000 hours is estimated for many commercially available HDDs. Typical
commercial use of HDDs would give these disks a replacement life of five years. With improvements
such as fluid/ceramic spindle bearings, surface lubrication of disks, and special head parking
108
techniques made on the most recent desktop HDDs, the life of HDDs may be somewhat longer.
However, there is no reliable testing of the life span of unused HDD and it would be astute to plan
to replace the disks in such a working system within 5 years.
6.3.20 Monitoring of Hard Disk Media
6.3.20.1An indication of imminent disk failure may be an increase in bad data blocks. It is typical for the latest
disks to show bad block errors even from new and most data systems manage the bad blocks by
reassigning the address of that block. However, if the quantity of bad blocks increases it may indicate
that the disk is beginning to fail. Software exists which will provide a warning of increased bad data
blocks, as well as measuring other physical characteristics that may indicate disk problems.
6.3.21 HDD technologies
6.3.21.1There are four main methods of connecting HDDs and other peripheral devices to computers, USB
(Universal Serial Bus), IEEE 1394 (Firewire), SCSI (Small Computer System Interface) and SATA/ATA
(Serial Advanced Technology Attachment/AT Attachment). They each have particular advantages
in certain situations. USB and Firewire are planned to be all-purpose buses that can be used to
connect to personal computer a HDD as well as digital video camera or MP3 player. SCSI and
SATA/ATA are mainly used to connect hard disk drives to a computer or disk storage system.
6.3.21.2SCSI and its successor SAS (Serial Attached SCSI) interface allows faster writing and reading speeds,
and facilitates access to larger numbers of drives than the SATA/ATA drives. SCSI disks can accept
multiple commands at once on a SCSI bus and does not suffer from request queues like SATA/ATA.
The SATA/ATA drives are comparatively cheaper. The read access speed is largely the same and in
an audio context neither interface will limit the operation of the digital audio workstation (DAW)
more than the other. The performance difference of SCSI/SAS and SATA drives can have meaning in
heavily utilised centralised hard disk storage system.
6.3.21.3Fibre Channel (FC) SCSI/SAS drives are mainly used in demanding use in enterprise or business
systems while the cheaper SATA drives are more used in the personal market, but they are also
increasingly used in enterprise and business systems to offer more cost-effective storage capacity
e.g. in archival storage. In archival storage, the actual decision between (FC) SCSI/SAS and SATA
technology is dependent on the actual load of the system. If a system is used to archive small or
medium amounts of content that is not accessed intensively a SATA based solution might well be
enough. The actual decision must be based on clearly identified demands and negotiations with one’s
storage provider.
6.3.21.4USB and Firewire connected disk can be used to transfer content from one environment to another,
but since they are rather unreliable, difficult to monitor and easy to loose they should not be used
for archiving even though their pricing may seem very attractive.
6.3.21.5The interface is not a completely consistent indication of the reliability and performance of a
given drive or storage system and the purchaser should be more aware of other operating and
configuration parameters of a storage system. It seems to be the case that more reliable drives are
associated with the FC SCSI/SAS interface. Nonetheless, HDDs are not in themselves permanently
reliable, and all audio data should be backed up on suitable tape (see 6.3.5 Data Tape Performance).
(For further discussion see Anderson, Dykes and Riedel 2003).
109
6.3.21.6There is one emerging storage technology which may have a prominent position in the near future.
Solid-state storage in form of flash memory is developing as a alternative to moving disks and has
already become an alternative to a HDD in laptop PCs. Some storage manufacturers have also
introduced flash drives in their low cost or midrange storage systems and are planning to introduce
flash drives in their high end systems too. Even though flash storage still has some challenges in
storage reliability to overcome it might become a viable solution to storage needs of archival
community; its price per gigabyte is becoming competitive, it is more environmentally friendly due
to lower demand for power, and it does not have moving parts, which could mean longer life time
of storage units. A life time of ten years instead of five years for a storage unit could mean lower
investment and management costs for an archivist since every other migration to the next storage
technology could be skipped. In terms of read and write performance flash storage is already
comparable with HDD technology.
6.3.22 Hierarchical Storage Management (HSM)
6.3.22.1The OAIS Functions of Archival Storage embeds the notion of Hierarchical Storage Management
(HSM) in the conceptual model. At the time OAIS was written the situation where large amounts
of data could be affordably managed in other ways was not envisaged. The practical issue that
underpins the need for HSM is the differing cost of storage media, e.g. where disc storage is
expensive, but tape storage is much cheaper. In this situation HSM provides a virtual single store
of information, while in reality the copies can be spread across a number of different carrier types
according to use and access speeds.
6.3.22.2However, the cost of hard disc has fallen at a greater rate than the cost of tape, to the point where
there is an equivalency in price. Consequently the use of HSM becomes an implementation choice.
Under these circumstances a storage system which contains all of the data on a hard disc array, all
of which is also stored on a number of tapes, is a very affordable proposition, especially for digital
storage systems up to 50 terabytes (and rising every year). For a smaller digital storage facility a fully
functional HSM is consequently unnecessary and instead what is required is a much simpler system
which manages and maintains copy location information, media age and versions and completely
replicates the stored data on hard disc and on tape.
6.3.22.3For medium to large digital storage systems the need for HSM storage systems remains and
continues to be amongst the very expensive components of the digital storage systems.
6.3.23 File Management Software in smaller systems
6.3.23.1 The purpose of file management software in systems where the entire archive is replicated both
on hard disc and tape is to keep track of the location, condition, accuracy and age of the tape
copies. This basic backup functionality is a lower cost alternative to a classic HSM and may, at least in
theory, be more reliable for small systems. However, as the large scale HSM represents a significant
market, research and development has been supported by the industry in this area. Small scale file
management software is being developed amongst the open source software development community.
These include such systems as three most popular open source NAS applications, FreeNAS, Openfiler
and NASLite, and the Advanced Maryland Automatic Network Disk Archiver (AMANDA). As with all
such open source solutions, the onus is on the user to test the suitability and reliability of such systems,
and without further development this publication makes no specific recommendation.
110
6.3.24 Verification and retrieval
6.3.24.1In some commercial software, tape read/write error can be reported automatically during the
data backup and verification process. This function is normally implemented with cyclic redundancy
check, a technology using checksum against data to detect errors for transmission or storage. It
is recommended that an error checking function should be implemented in any archival storage
system. Error checking is difficult to implement in open source because that capability is linked
to specific hardware. A commercially available stand-alone LTO Cartridge Memory Reader is the
“Veritape” from MPTapes, Inc. and recently, Fuji Magnetics announced a Chip Reader Diagnostics
System for LTO-Cassettes, bundled with software.
6.3.25 Integrity and Checksums
6.3.25.1A checksum is a calculated value which is used to check that all stored, transmitted or replicated
data is without error. The value is calculated according to an appropriate algorithm and transmitted
or stored with the data. When the data is subsequently accessed, a new checksum is calculated
and compared with the original, and if they match, then no error is indicated. Checksum algorithms
come in many types and versions and are recommended, and standard, practice for the detection of
accidental or intentional errors in archival files.
6.3.25.2The cryptographic versions are the only type that have a proven record of trust when protecting
against intentional damage to data, and even the simplest of these are now compromised. It has
been recently shown that there are ways of creating meaningless bits that will calculate as a given
MD5 checksum. This means that an external or internal intruder may replace digital content with
meaningless data and that this attack will go unnoticed by the error checking management system
until the files are required for use and opened. MD5, although still useful for transmission purposes,
is 124 bit and should not be used where security is the issue. SHA-1 is another cryptographic
algorithm that is under threat of being compromised, and which it has already been shown can,
in theory, be circumvented. The length of SHA-1 is 160 bit: SHA-2 comes in versions with 224,
256, 384, and 512 bit lengths, and are algorithmically similar to SHA-1. The steady growth of
computational power means that these checksums may, in the long run, be compromised as well.
6.3.25.3Even with these compromises, a checksum is a valid approach to detecting accidental errors, and if
incorporated into a trusted digital repository, may well be sufficient to uncover intentional damage
to data files in low risk scenarios. However, where risks exists, and perhaps even where they do not,
monitoring checksums and their viability must be part of preservation planning.
111
6.4 Digital Preservation Planning
6.4.1 Introduction
6.4.1.1 Once the action has been taken to convert the audio content to a suitable digital storage format for
storage on a digital storage system, as defined earlier in this document, there is still a requirement to
manage the ongoing preservation of the content. Section 6.3 Archival Storage includes a description
of the issues surrounding management of the byte stream, i.e. ensuring that the digitally encoded
data retains its logical structure through management of the storage technology.
6.4.1.2 There is, however, another aspect to the preservation of digital information, and that is ensuring that
it is still possible to access the content encoded in those files. OAIS calls this function “preservation
planning”, and describes it as “the services and functions for monitoring the environment… and
providing recommendations to ensure that the information stored… remains accessible to the
Designated User Community over the long term, even if the original computing environment
becomes obsolete” (OAIS 2002:4.2).
6.4.1.3 Preservation planning is the process of knowing the technical issues in the repository, identifying
the future preservation direction (pathways), and determining when a preservation action, such as
format migration, will need to be made.
6.4.2 Future Digital Pathways
6.4.2.1 When a file format becomes obsolete and is at risk of becoming inaccessible due to the
unavailability of appropriate software to access the content, there are basically two approaches
that can be made; migration, or emulation. In migration the file is modified, or migrated to a new
format, so that the content can be recognised and accessed using the available software of the
time. In emulation, the access or operating software is modified or designed so that it will open
and play the obsolete audio file format on a new system which would not otherwise be able to
open the content.
6.4.2.2 Our current understanding leads us to believe that for simple discrete files, such as uncompressed
audio files, the most likely approach will be migration but this is not certain and all digital storage
approaches and systems should be flexible enough to be responsive to the changing environment.
Adequate preservation metadata as described in the PREMIS recommendations or the explicit
file typing (including versioning) in BWF/AES31-2-2006 fields will support either approach, as will
the standards being developed in AES-X098B which will be released by the Audio Engineering
Society as AES57 “AES standard for audio metadata — audio object structures for preservation
and restoration”. Harvard University is developing a toolkit which supports the population of the
necessary fields which will be released in open source.
6.4.2.3 This aspect of digital preservation is the strongest argument for an absolute adherence to the
standard format described. The large investment the audio and IT industries have made in the
standard audio format (.wav) means that the requirement for professional software tools which
will enable the continued access to content will help to ensure that the sound archive can manage
access to their collections. Likewise, the large investment in a single format will also help support
the continuance of that format for the longest period, as the industry will not change an entrenched
format without significant benefits.
112
6.4.3 Motivating Factors and Timing
6.4.3.1 Though the wise choice of standard formats, and an observance of industry practices will delay
the eventuality, the day will come where it will be necessary to undertake a preservation action of
some type which will be needed to maintain access to the audio content stored. The issue for sound
archivists concerned with their digital content will be determining when to undertake that step and
what precisely to do.
6.4.3.2 A number of initiatives are being developed to help support this need. These include the Global
Digital Format Registry (GDFR http://hul.harvard.edu/gdfr/), which exists to support “the effective
use, interchange, and preservation of all digitally-encoded content.” Other services provide
recommendations about suitable format, such as those provided by the Library of Congress (US)
or The National Archives (UK).
6.4.3.3 The factors which will motivate a sound archivist to undertake some sort of preservation action
will be the recognition that new software no longer supports the old format, and the industry as
a whole moving to select a new format. Knowledge of the events that herald change comes from
expert understanding of the technology, the industry and the market and sound archivists are well
advised to take heed of the recommendations services such as those noted above.
6.4.3.4 Software and services under development, such as the Automatic Obsolescence Notification
System (AONS), will provide advice to collection managers on when changes have occurred in the
market requiring action (https://wiki.nla.gov.au/display/APSR/AONS+II+Documentation).
The implementation of such services will occur in parallel with the development of the GDFR.
113
6.5 Data Management and Administration
6.5.1.1 Data Management, in the OAIS, is the services and functions for populating, maintaining, and
accessing both descriptive information which identifies and documents archive holdings and
administrative data used to manage the archive, in other words the catalogue of content and the
statistical record of data content.
6.5.1.2 Administration, in the OAIS, is the services and functions for managing system configuration,
monitoring operation, providing customer service and updating archival information. It is also
responsible for management processes such as negotiating submission agreement with producer,
auditing submission, control physical access, establishing and maintaining archive standards.
6.5.1.3 The management and administration of the digital repository and archival system provides services
that allow the sustainability of the system and the preservation of the content stored therein. A
requirement of an archival digital storage system would include the ability to interrogate the system
to produce result sets of holdings, access usage statistics, contents summaries including sizes and
other necessary technical and management information. The data management and administration
is critical to a sustainable archival system because this functionality ensures that files preserved and
accessed are properly found and identified.
6.5.1.4 It is within this section of the digital storage and preservation system that control over access
to content, or security control, is implemented. Many repository software systems incorporate
approaches to implementing policies which are stored and managed by the system. It is important to
recognise that the rights management information, like the audio content itself, must outlast the system
used to store it, and so be transferable to any future replacement preservation and storage system.
Information which is encoded in XACML (eXtensible Access Control Markup Language) for example, is
both more universally enforceable, and transferable to other systems. XACML is a declarative access
control policy language implemented in XML and a processing model, describing how to interpret the
policies. XACML is managed by the OASIS standards group (http://www.oasis-open.org/committees/
tc_home.php?wg_abbrev=xacml ).
6.5.1.5 When selecting, establishing and installing a digital preservation system one of the critical tests should
be to determine if the administration of the proposed system is within the capabilities of the host
institution. The capability and breadth of functions of a system is often linked with the complexity of
use and installation. A system which cannot be adequately managed and maintained is a major risk
to the content it manages. It is therefore important that the long term management of a system take
account of the available technical expertise required to sustain its use.
114
6.6 Access
6.6.1 Introduction
6.6.1.1 The OAIS Reference Model defines “access” as the entity that “provides the services and functions
that support consumers in determining the existence, description, location and availability of
information stored in the OAIS, and allowing consumers to request and receive information
products.” In other words, access is the mechanisms and process where content is found and
retrieved. IASA-TC 03 “The Safeguarding of the Audio Heritage: Ethics, Principles and Preservation
Strategy” makes the point that “the primary aim of an archive is to ensure sustained access to stored
information”. The preservation of the content is a prerequisite to sustained access to the content,
and in a well planned archive access is a direct outcome of it.
6.6.1.2 In its simplest form, access is the ability to locate content and, in response to an authorised request,
allow retrieval of the content for listening, or possibly, as long as the rights associated with a work
allow it, creating a copy that can be taken away. In the connected digital environment access can be
provided remotely. Access, however, is more than just the ability to deliver an item. Most technically
constructed archival systems can deliver an audio file on request, but a true access system provides
finding and searching capability, delivery mechanisms and allows interaction and negotiation
regarding content. It adds a new dimension to access beyond that of conquering distance. In
this new services based model of retrieval, access could be considered a dialogue between the
provider’s system and the user’s browser.
6.6.2 Integrity in On Line and Off Line Access Environments
6.6.2.1 Prior to the existence of remote access in the online environment, such things as authenticity and
integrity were established by individuals in the reading rooms and listening posts of the collecting
institutions. The content was delivered by representatives of institutions whose reputation spoke
for the integrity of the content. Original materials could be retrieved for examination if the copies
were questioned.
6.6.2.2 The online environment still relies to some extent on the trusted nature of the collecting
institution, however, an unambiguously original item can never be provided online, and the
possibility of undetected tampering or accidental corruption exists within the archive and
distribution network. To counter this, various systems exist which mathematically attest to the
authenticity or integrity of an item or work.
6.6.2.3 Authenticity is a concern with knowing that something has originated from a particular source.
The trusted nature of the institution creating the content attests to the processes, and a certificate
authority is issued which a third party can use as a guarantee of authenticity. Various systems exist
and are valuable where this could be an issue.
6.6.2.4 Integrity refers to a wish to know whether an item has been damaged or tampered with.
Checksums represent the common way of dealing with integrity, and are valuable tools in both
the archive and the distribution network (see 6.3.23 Integrity and Check sums). However, as is
discussed in 6.3.23, checksums are fallible, and their use requires monitoring on behalf of the
archive of latest developments.
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6.6.3 Standards and Descriptive Metadata
6.6.3.1 Detailed, appropriate, organised metadata is the key to broad exposure and effective access. In
Chapter 3 Metadata, a detailed discussion of metadata in many of its forms and requirements
is undertaken, and this should be referred to in developing a delivery system. Ambitious access
facilities, using, for example map interfaces or timelines, will only function if there is metadata to
support it in a structured and organised form.
6.6.3.2 The most cost effective way to manage and create the appropriate metadata is to ensure the
requirements for all the components in the delivery system are established prior to the ingest of
the content. In this way the metadata creation steps can be built into the pre-ingest and ingest
workflows. The cost of creating a minimal set, as discussed in Section 7.4, is the extra task of adding
and structuring the metadata in a system which has already been created.
6.6.4 Formats and Dissemination Information Packages (DIP)
6.6.4.1 The Dissemination Information Package (DIP) is the Information Package received by the Consumer
in response to a request for content, or an order. The delivery system should also be able to deliver
a result set or a report from a query.
6.6.4.2 Web developers and the access “industry” have developed delivery systems based, naturally, around
delivery formats. Delivery formats are not suitable for preservation, and generally, preservation
formats are not suitable for delivery. In order to facilitate delivery, separate access copies are
created, either routinely, or “on demand” in response to a request. Content may be streamed,
or downloaded in compressed delivery formats. The quality of the delivery format is generally
proportional to its bandwidth requirements, and collection managers must make decisions about
the type of delivery formats based on the user requirements and the infrastructure to support
delivery. QuickTime and Real Media formats have proven to be popular streaming formats and MP3
(MPEG 1 Layer 3) a popular downloadable format which may also be streamed. There is no
requirement to select only these formats for delivery, and many collection delivery systems provide
a choice of formats to the user.
6.6.4.3 For some types of material it may be necessary to create two master WAV files: one, a preservation
or archival master that replicates exactly the format and condition of the original the second, a
dissemination master that may have been processed in order to improve the audio quality of the
content. A second master will allow the creation of dissemination copy as required. It is expected
that distribution formats will continue to change and evolve at a faster rate than master formats.
6.6.5 Search Systems and Data Exchange
6.6.5.1 The extent to which content can be discovered sets the limit on the amount of use of the material.
In order to ensure broad usage it is necessary to expose content through various means.
6.6.5.2 Remote databases can be searched using Z39.50, a client-server protocol for searching and
retrieving information. Z39.50 is widely used in the Library and Higher education sector, and
its existence predates the web. Given the extent of its use, it is advisable to establish a Z39.50
compliant client server on databases. However, this protocol is being rapidly replaced in the
web environment by SRU/SRW (Search/Retrieval via a URL and Search/Retrieve Web service
respectively). SRU is a standard XML-focused search protocol for Internet search queries,
utilizing CQL (Contextual Query Language), a standard syntax for representing queries
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(http://www.loc.gov/standards/sru/). SRW is a web service that provides a SOAP interface for
queries in partnership with SRU. Various open source projects support SRU/SRW in relation to the
major open source repository software such as DSPACE and FEDORA.
6.6.5.3 OAI-PMH (Open Archives Initiative Protocol for Metadata Harvesting) is a mechanism for
repository interoperability. Repositories expose structured metadata via OAI-PMH which is
aggregated and used to support queries on the content. OAI-PMH nodes can be incorporated into
the common repositories. OAI-ORE (Object Reuse and Exchange) will be important for the sound
and audiovisual archiving community as it addresses the very important requirement to be able
to deal efficiently with compound information objects in synchronisation with Web architecture.
It allows the description and exchange of aggregations of Web resources. “These aggregations,
sometimes called compound digital objects, may combine distributed resources with multiple media
types including text, images, data, and video”. http://www.openarchives.org/
6.6.5.4 In order for the sophisticated online environment to work it is necessary to have interoperable
metadata and content. This means that there must be some shared understanding of the attributes
included, a general schema which is able to operate in a variety of frameworks, and a set of
protocols about exchanging content. This is best achieved, as is always in the digital environment,
by adhering to the standards, schemas, frameworks and protocols recommended and avoiding
proprietary solutions.
6.6.6 Rights and Permissions
6.6.6.1 It is important to note that all access is subject to the rights established in the items and the
permission of the owner to use the content. Various rights management approaches exist, from
“fingerprinting” the content, to managing the permissions of various individual to access, the physical
separation of the storage environment. The particular implementation rights system will depend on
the type of content, the technical infrastructure and the owner and user community and it is beyond
the scope of this document to define or describe a particular approach.
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Chapter 7: Small Scale Approaches to Digital Storage Systems
7.1
Introduction
7.1.1.1 It is possible to build small scale digital storage systems to meet the requirement of archives with
smaller collections and a small recurrent budget. Until recently, only large and comparatively wealthy
organisations with sound archives were able to digitise their holdings on a large scale and store
them by means of Digital Mass Storage Systems comprising of managed hard disk and data tape.
These systems tended to be large and expensive dedicated audio and audio-visual storage systems.
In more recent years many national sound archives and large libraries have, with the university and
higher education sector, initiated and supported the development of open standards and open
source software which supports digital archiving widely. These enterprise systems are now the
backbone and the model for all forms of digital archiving. Audio archiving benefits by using these
systems and importing our own discipline specific knowledge to them.
7.1.1.2 At the same time as open source and other low cost software solutions are appearing on the
market, the cost of data tapes are decreasing, and hard disk drives (HDD) are dropping at an even
greater rate. It is now possible to undertake digital archiving of a far more professional character
than the inherently risky single carrier target formats such as recordable CD or DVD.
7.1.1.3 This chapter of the guidelines describes how a small scale digital repository meeting the
requirements of an OAIS might be established and managed. Chapter 6, Preservation Target Formats
and Systems, contains much that is pertinent to this chapter, as does Chapter 3 Metadata, and
Chapter 4 Unique and Persistent Identifiers.
7.2
Approaches to Small Scale Digital Archiving
7.2.1 Funding and Technical Knowledge
7.2.1.1 It is quite possible to build a low cost digital preservation system, but this cannot be achieved
without at least a small level of technical knowledge and some recurrent resources, albeit at a low
level, to make it sustainable. Regardless of how simple or robust a system is, it must be managed and
maintained, and it will need to be replaced at some time or risk losing the content it manages.
7.2.1.2 “Digital preservation is as much an economic issue as a technical one. The requirements of
ongoing sustainability demand at their base a source of reliable funding, necessary to ensure that
the constant, albeit potentially low level, support for the sustainability of the digital content and its
supporting repositories, technologies and systems can be maintained for as long as it is required.
Such constant funding is not at all typical of the many communities that build these digital collections,
many of which tend to be grant funded on an episodic basis. There is therefore a need to develop
costing models for sustainability of digital materials according to the specific requirements of the
various classes of content, access and sustainability.” (Bradley 2004).
7.2.1.3 It is inevitable and unavoidable that the system and its hardware and software components will
require maintenance and management which will demand both technical knowledge and dedicated
funds. Any proposal to build and manage an archive of digital audio objects should have a strategy
which includes plans for the funding of ongoing maintenance and replacement, and a listing of the
risks associated with the loss of technical expertise and how that will be addressed.
7.2.2 Alternative Strategies
7.2.2.1 In the event that there is no adequate way to manage the risks described in the section above an
archive may decide to continue with the preservation and digitisation of their collection to look to
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Small Scale Approaches to Digital Storage Systems
partnerships to manage the storage risks. An archive may choose to distribute the risk in a number
of ways, including; by forming local partnerships so that content is distributed between a number
of related collections; by establishing a relationship with a stable well funded archive; by engaging a
commercial supplier of storage services (see Section 6.1.6 Long Term Planning).
7.2.2.2 To effectively take advantage of any of the approaches described it would be necessary to establish
an agreement about what data and content would be exchanged between the partners, and the
form it would take. This agreement should be established well before the need to take advantage of
it might occur. An agreement about exchange packages would consider all the relevant information
necessary to continue the archival role undertaken by an archive. This would include the data that
makes up the audio object itself in its archival form, the technical metadata, descriptive metadata, the
structural metadata, rights metadata, and the metadata created to record provenance and change
history. It would need to be packaged in a standard form so that it could be used to recreate the
archive if data was lost, or so that another archive could take up the role of managing content if that
was deemed necessary.
7.2.2.3 The tools to produce such profiles exist using, for example, Metadata Encoding and Transmission
Standard (METS), a Library based approach that is widely used, are available. Whether this or other
strategies are used, agreement about their form is critical to the success of the strategy. Whether this
is used to support remote content replication or to support federation of cooperating archives, the
agreement about standard form and exchange is a most effective preservation strategy, spreading
the risk of failure, due to natural or man made disaster or just lack of resources at a critical time in
the life-cycle of the digital audio object.
7.3
Description of System
7.3.1.1 In Section 6.1.4 Practical Aspects of Date Protection Strategies, the need to address the functional
categories defined in the Reference Model for an Open Archival Information System (OAIS, ISO
14721:2003) is argued. The same issues apply to both large and small scale collections as this
framework is critical to the development of modular storage systems with interoperable exchange
of content. The following section which deals with small scale systems adopts the major functional
components of the OAIS reference model to assist in the analysis of the available software and to
develop recommendations for necessary development. They are Ingest, Access, Administration, Data
Management, Preservation Planning and Archival Storage.
7.3.1.2 The system described consists of some form of repository software which manages the content,
at least a minimum set of metadata, as well as hardware, with some recommendations on manual
approaches to manage the data’s integrity. The hardware section outlines broadly two situations
under which small scale storage systems may be implemented; a single operator digitising onto a
single storage device, and a situation where more than one operator requires access to the storage
device. Either system assumes compliance with all other components mentioned in the Guidelines,
including appropriate analogue to digital converters, adequate sound cards, digital audio workstations
(DAW) and appropriate replay devices.
7.3.1.3 The following information describes systems and software that might support a small scale collection
as though an institution or collection were undertaking all the tasks. It is important to recognise that
the approaches described below do not have to be undertaken by one collection. It is possible to find
partners and commercial providers who might support some or all of the tasks described below.
It is equally important to recognise that all of these tasks form the complete preservation and archival
package and must be undertaken by someone whether locally managed or distributed.
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7.3.2 Repository Software
7.3.2.1 A well designed piece of repository software will support a number of the functions identified in
the OAIS. There are both commercial providers of the software and open source. The advantage
of commercial software is the provider is expected to make the system work, however, these
commercial systems have ongoing expenses and may lock the user into proprietary systems from
which it is hard to escape. Open source software’s main advantages are that it is free, and the
developers adhere to open standards and frameworks which will allow the extraction of content in
future upgrades. Its disadvantage is that, though open source communities are helpful, support is the
responsibility of the user. It is however, possible to find commercial providers who provide a support
service for the open source solutions.
7.3.2.2 Most of these repository software systems will support the tasks identified in access, administration,
data management and some aspects of ingest. At the time of writing preservation planning and
archival storage is generally not supported by repository software, the former being very often
technology or format specific, and the latter dependant on hardware. They are discussed separately
in the following sections.
7.3.2.3 Two types of open source software are briefly described, however, this software is under constant
development, and the claims and comments made below should be checked against the latest
developments made by the software providers. The software described are DSpace and FEDORA.
7.3.2.4 The DSpace repository platform is a very popular and widely adopted repository within the higher
education and research sectors, although knowledge of its use within the museums and cultural heritage
sectors is limited but growing. One of the reasons for the popularity of DSpace is that it is relatively easy
to install and maintain, and has a ready made user-interface that integrates data management and access
functions within the system’s architecture. DSpace has a strong international developer community that
has evolved to support DSpace and new features are being added constantly.
7.3.2.5 One of the strengths of DSpace is its integrated feature set enabling institutional users to quickly
establish a repository and then start adding new items to the collection. This strength, however, is
also one of its major weaknesses, in that DSpace has evolved into a monolithic software application,
and complex code base, that introduces potential scaling and capacity constraints for some large
institutional users. This presents no problems for most small to medium scale collections, and is
probably not an issue for any digital audio collection. DSpace currently uses a qualified version of the
Dublin Core schema based on the Dublin Core Libraries Working Group Application Profile (LAP)
7.3.2.6 FEDORA (Flexible Extensible Digital Object and Repository Architecture) is an increasingly popular
repository system that is designed as a base software architecture upon which a wide range of
repository services can be built, including preservation services. Compared to the speedy adoption
of DSpace, FEDORA has been slower to gain adopters because it lacks a dedicated user-interface
and access service out-of-the-box. There are a number of commercial and opens source providers
of web-based front-ends for FEDORA.
7.3.2.7 The main strengths of FEDORA are its flexible and scalable architecture. The experiences of
institutional adopters indicate that FEDORA can scale to cope with large collections, yet is
sufficiently flexible to store multiple types of digital items and their complex relationships. There are
few limitations to the features that can be added to FEDORA, whilst still remaining interoperable
with other software applications and systems. It can be configured to support virtually any of the
metadata profiles through METS ingest capabilities. The main disadvantage of FEDORA is the high
level of software engineering expertise required to contribute to its core development, and it is not
readily installed and implemented “out-of-the-box” (Bradley, Lei and Blackall 2007).
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7.3.2.8 Tools have been developed to migrate content from DSpace to FEDORA and visa-versa, which
theoretically negates any future compatibility issues and supports sharing and other workflows (see
http://www.apsr.edu.au/currentprojects/index.htm )
7.4
Basic Metadata
7.4.1.1 Chapter 3 Metadata, outlines the requirements of documentation and management of a collection.
As has been stated, metadata is pivotal to all aspects of the life cycle of a digital audio object, and
paying strict attention to describing all aspects of the collection is one of the more important
steps in its preservation. A detailed metadata record of all technical, process, provenance and
descriptive aspects is a vital part of the preservation process. However, it is recognised that there
is often a technical imperative to preserve audio collection material, and that this may well be
before a metadata management system or policy has been developed. The following very basic
recommendations are intended as a first step, a collection of data which is necessary to manage the
file, or which must be captured or it would otherwise be lost:
7.4.1.1.1 Unique Identifier: Should be structured, meaningful and human readable as well as unique.
A meaningful identifier can also be used to relate objects like: master or preservation files
and distribution copies, metadata records, series, etc where a sophisticated system will
manage that in the metadata.
7.4.1.1.2 Description: Description of the sound sequence. A small amount of text to simply identify
the content of the audio file.
7.4.1.1.3 Technical Data: Format, sampling rate, bit rate, file size. Though this information can be
acquired later, making it an explicit part of the record allows management and preservation
planning of the collection.
7.4.1.1.4 Coding History: In BWF a number of discrete lines of information describing the original
item and the process and technology of creating the digital file that is being archived.
(See also 3.1.4 Metadata).
7.4.1.1.5Process errors: Any error data which the transfer system can collect which describes
failings in the transfer process (e.g. uncorrectable errors in CD or DAT transfers).
7.4.1.2 The information described in Unique Identifier, Description, and Technical Data can be recorded
in Dublin Core records or the BWF headers. Coding History and Process errors can be recorded
in the BeXT chunk of the BWF headers or in related XML encoded documents. The date, and if
necessary, time of transfer should be recorded into the BWF header, and the date, and if necessary,
time of ingest into the repository should be recorded in the metadata management in the
repository. In some circumstances the timestamp information that relates components of a multipart recording will be mandatory. It is generally advisable to include time and date information with
every event or digital object.
7.5
Preservation Planning
7.5.1.1 Preservation planning, as has been discussed, is the planning and preparation which goes to ensure
that the digital audio object remains accessible over the long term, even if the computing storage
and access environment becomes obsolete. Preservation planning for a small scale collection which
is interested only in the preservation of its own digital audio objects is a relatively straightforward
task. The metadata captured above informs the decisions about preservation by making clear the
relationship between the original and the preservation copy in the digital repository. The technical
information helps with planning. The choice of BWF as the preservation format is made to ensure
the longest time possible before any format migration is necessary. It remains only for the collection
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managers and curators to maintain knowledge of the changes occurring in the digital archiving
domain through contact with such associations as IASA.
7.6
Archival Storage
7.6.1.1 The archival storage system sits underneath the repository, technically speaking, and incorporates a
suite of sub-processes such as storage media selection, transfer of the Archival Information Package
(AIP) to the storage system, data security and validity, backup and data restoration, and reproduction
of AIP to new media.
7.6.1.2 The basic principles of archival storage can be summarised as follows
7.6.1.2.1 There should be multiple copies. The system should support a number of duplicate copies
of the same item.
7.6.1.2.2 Copies should be remote from the main or original system and from each other. The
greater the physical distance between copies the safer in the event of disaster.
7.6.1.2.3There should be copies on different types of media. If all the copies are on a single type of
carrier, such as hard disc, the risk of a single failure mechanism destroying all the copies is
great. The risk is spread by having different types of carriers. IT professionals commonly use
data tape as the second (and subsequent) copy.
7.6.1.3 The major cost in the data storage systems is not the hardware, but the Hierarchical Storage
Management (HSM) System. The OAIS Functions of Archival Storage embeds the notion of HSM in
the conceptual model. At the time OAIS was written the situation where large amounts of data could
be affordably managed in other ways was not envisaged. The practical issue that underpins the need
for HSM is the differing cost of storage media, e.g. where disc storage is expensive, but tape storage is
much cheaper. In this situation HSM provides a virtual single store of information, while in reality the
copies can be spread across a number of different carrier types according to use and access speeds.
7.6.1.4 However, the cost of disc has fallen at a greater rate than the cost of tape, to the point where
there is an equivalency in price. Consequently the use of HSM becomes an implementation choice.
Under these circumstances a storage system which contains all of the data on a hard disc array, all of
which is also stored on a number of tapes, is a very affordable proposition, especially for a small to
medium sized digital audio collection. For this type of system a fully functional HSM is unnecessary
and instead what is required is a much simpler system which manages and maintains copy location
information, media age and versions (Bradley, Lei and Blackall 2007).
7.7
Practical Hardware Arrangements
7.7.1.1 The following information describes how a practical system might be implemented. As has already
been discussed above, the assumption is that all of the audio archival data will be stored on hard
drive and all of the audio archival data will also be mirrored on data tape such as LTO.
7.7.2 Hard Disk drives
7.7.2.1 A common and affordable approach to data storage on disk is to connect to a cluster of HDDs
(hard disk drive) arranged in a RAID array (see section 6.3.14 Hard Disk Drives). RAID level 1 is little
more than two drives mirrored; keeping two copies of the data on different physical hardware; if one
disk fails it is available on the other drive. Higher level RAID arrays (2 to 5) implement increasingly
complex systems of data redundancy and parity checking that ensures the data integrity is maintained.
The higher level RAID arrays achieve the same level of security as level 1, or mirroring, but with
significantly less storage space. RAID 5, for example, may have a 25% storage loss (or less depending
on implementation), when compared to 50% for RAID 1. Sophisticated arrays are widely available.
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7.7.3 Tape Backup
7.7.3.1 No single component of a digital system can be considered reliable, instead the reliability of the
system is achieved through multiple redundant copies at every stage. The final and most important
component in the storage chain is the data tape. In the recent past LTO has gained popularity for
this purpose (see section 6.3.12 Selection and Monitoring of Data Tape Media), however other data
tape formats may be appropriate depending on the particular circumstance.
7.7.3.2 All data on disk storage should be duplicated on a suitable storage tape. A minimum of two sets
of data tapes must be produced, to be stored physically in different places. As it is not unusual for
the second set of tapes to be required in the restoration of the data many established archives
make three sets of copies, two to be kept near the system for ease of access and a third set stored
remotely to protect against physical disasters. It has become customary that the separate sets of
data tapes should be made using different products of which a considerable amount of the same
batches are bought at one time. This renders quality control and rescue measures easier, once a
batch of a given product should fail. Appropriate volume management software will aid in the back
up and retrieval process especially if the system incorporates a number of storage devices.
7.7.3.3 Error checking is difficult to implement in open source and low tech solutions because that
capability is linked to specific hardware. Nonetheless, a low-tech possible alternative to proper error
testing is described in the following paragraph. The data management software has a catalogue (with
a printer attached). The hard disc (in RAID) contains a complete set of data. All data is copied onto
identical tape copies. There are at least two copies. As data is copied onto a tape, a unique identifier
is printed onto a label (human readable) which is attached to the tape. The same identifier can be
recorded onto the header of the tape. The data management system can be scripted to prompt
the user to find and insert the tape identified by the system. Rather than checking the tape for
errors, the system will verify the content of the tape against the hard disc. The hard disc can check
the veracity of its own data content and is aware of any failings itself. If the verification of the tape
fails, the system can produce a new tape from the hard disc. Assuming 20 terabytes of storage, the
system would verify two tapes a day, every tape and its duplicate can be verified three times per
year. In the event of a disc failure requiring the data tapes to replace it, there will be two tapes which
have been checked within the previous four months. The risk that both tapes and the hard disc
would fail is very low.
7.7.4 Single (or Double) Operator Storage System
7.7.4.1 The simplest archival storage system would be to attach a separate RAID array containing only the
audio data to the primary DAW (digital audio workstation). This configuration is only possible for
institutions with one operator in the digitising process. A requirement for the success of this approach
is a well structured plan for digitisation and a dedicated disk array so as the work can be carried
out continuously without major interruptions. This will ensure that the HDD attached to the DAW
continuously copies to tape whenever the amount of data to fill the target medium is reached.
7.7.4.2 If two operators and workstations are undertaking the digitisation tasks it will be necessary to
provide access to a shared drive or drives. The sharing of such resources can be achieved by
defining one of the computers as the server, and configuring it so that it manages the drives, and
implementing a single wire sharing capability. Such an approach is relatively easy to implement and
allows sharing between two operators, though it requires some procedural agreements to avoid
conflicts. Logical organisation of data and strict naming procedures are a necessity of small scale
manual storage systems.
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7.7.4.3 If a system were established of the size described here. It might be the case that it would be more
effective to establish a partnership with a larger archivally established institution, or to contract a
storage service provider. Nonetheless, the approach above is possible.
7.7.5 Multiple operator storage system
7.7.5.1 For any number of connections greater than two, a networked system of data storage and backup
should be implemented. Such a networked system allows access to multiple users in accordance with
the rules set down by the data management system. Small scale networks are relatively common and,
with the right level of knowledge, easy and affordable to implement. Reasonable quantities of storage
can be achieved with an enterprise level attached storage device. Storage technologies and products
can be split into three main types: direct-attached storage (DAS), network-attached storage (NAS)
and the storage area network (SAN). NAS has better performance and scalability than DAS and it is
cheaper and simpler to configure than SAN. NAS technology is, from a cost benefit view, the most
appropriate scalable technology for system of the size under discussion.
7.7.5.2 Most low cost NAS devices exhibit reduced bandwidth when compared to the more expensive
devices resulting in slower access times, or a lower number of allowable simultaneous access availability.
This should present no major problem to smaller collection as the requirement for simultaneous
access remains low, especially if MP3 derivatives of the preservation master copies are used for access.
7.7.5.3 A typical small scale networked storage system may comprise of a server class desktop computer
connected to a NAS device. The NAS would have the capability of mounting multiple hard disks in
a RAID array. An average low cost NAS would hold between 0.5 and 20 terabytes of disk storage
(noting the penalty for RAID is less storage than that indicated by the raw disk size). The digital audio
workstations (DAW) access the NAS via an Ethernet switch or similar device which, if configured
properly, has the effect of separating the storage facility from the office LAN (local area network) and
improves the security of the storage facility. The HDDs would be backed up onto data tape.
7.8
Risks
7.8.1.1 Automated storage systems can be configured to constantly copy and refresh data, discarding data
tapes which have become unreliable. Large-scale Digital Mass Storage Systems are professionally
designed and run by well resourced organisations which can afford and guarantee all necessary
measures for data security. With manual data back up and recovery systems the dangers of data
loss associated with self-designed and self-managed manual and semi-automated digitisation systems
cannot be overestimated. The responsibility for ensuring that the archived audio data remains valid
and accessible falls upon the individual, and requires that they physically check the data tapes on
a regular basis. This situation is specifically aggravated by the fact that most research and cultural
institutions are notoriously under-financed.
7.8.1.2 Though the design of such systems seems to incorporate a very high level of redundancy, one has to
bear in mind that the digital components and carriers may fail at any moment without any warning.
Therefore it is imperative to have at any stage of the digitisation process and the further storage at
the very minimum two copies of the linear archive file. Any flaw will inevitably lead to the loss of
a smaller or greater amount of data, however, if suitable strategies have been put in place, this will
not be fatal because the redundant copies are available. In view of the time consuming process of
transfer not to mention the inevitable losses of older materials, all efforts have to be made to avoid
the necessity of re-digitising materials as an outcome of an inconsistent security architecture or
careless conduct in the concrete approach.
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7.8.2 Complexity of the System
7.8.2.1 Once implemented and installed data storage systems are relatively easy to operate and maintain.
However, at the initial stages of implementation and at any subsequent problem or upgrade,
specialised IT support is strongly recommended to ameliorate the risk of poor set up.
7.8.3 Partnerships and Backup
7.8.3.1 As has already been discussed, a partnership which provides data backup capability with an
institution with established and trusted digital archival practices is a major manager of risk. A
network of repositories which can create and accept such organised packages of information will
be a most effective preservation strategy, spreading the risk of failure due to natural or man made
disaster, or just lack of resources at a critical time in the life-cycle of the digital object.
7.8.4 Cost and Scalability
7.8.4.1 A small scale system described above can be added to in order to allow the creation of larger
storage and management capabilities. Relatively small tape drives which can handle a number of data
tapes are available and larger scale robotic systems may make the system expandable. If HDD costs
continue to fall the cost of replacing and expanding the disk arrays remains affordable.
7.8.4.2 Partnerships between commercial suppliers and open source providers mean that the sophistication
of the repository software can be integrated with the safety of a commercial service provider.
DSpace and FEDORA, for example, have both released an open source system that operates with a
commercial storage solution company.
7.8.4.3 The cost of establishing a small scale data storage system may seem relatively high in comparison to
purchasing an individual CD burner, however, on a bit for bit comparison for the storage of more
than a few hundred hours of audio, the relative difference is greatly reduced when costing all the
requirements of an archive. In addition, a properly managed data storage facility is an altogether
more reliable system and will allow the future transfer of audio data to the next storage solution
when that inevitability occurs.
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Chapter 8: Optical discs
8.1
CD/DVD Recordables
8.1.1 Introduction
8.1.1.1 Recordable CD (CD-R) and recordable DVD (DVD-R/+R), have become integral in the recording
and distribution of many types of audio and audio-visual materials. Though the CD and DVD are now
only one of many types of more affordable and reliable storage technologies, the format remains
popular for many reasons, amongst them their ease of use and common familiarity. The CD was initially
marketed as the perfect permanent carrier, but this was soon shown not to be the case when many
of the early discs failed. Even though subsequent technological development has improved on many of
the early manufacturing faults, no credible claim can be made to permanence. In fact, digital archiving
experts commonly acknowledge that no carrier is permanent. Instead, the processes of acquiring
data, transferring to storage systems and managing and maintaining the data, and providing access and
ensuring the integrity of the stored information, presents a new range of risks that must be managed
to ensure that the benefits of digital preservation and archiving are realised. Failure to manage these
risks appropriately may result in significant loss of data value and content.
8.1.1.2 Recordable CDs and DVDs are often chosen as archival carriers, however, the risk of failure of a
storage system based on this type technology is high when compared to other approaches. An
integrated digital mass storage system with suitable digital repository management software is
recognised as the most appropriate for the long term sustainability of data. There may, however, be
circumstances where a collection curator may make a decision to use optical disc for storage.
8.1.1.3 Bearing in mind these constraints, it is possible to use recordable optical disks as reliable carriers for
a short period of time providing the following recommendations are carefully adhered to.
8.1.2 CD-R and DVD-R Recording Formats
8.1.2.1 There are two different approaches to the encoding of audio and video on recordable CDs
and DVDs, either as an audio “stream”, or as a data file. In the first of these approaches sound
is recorded as CD-DA formatted audio, which makes them playable in ordinary CD-players, or
to encode it in MPEG formatted DVDs, which may not all play in standard DVD-players. Stand
alone recorders will only record these formats, though computer based equipment may optionally
produce disks in these standard domestic forms. The use of these formats severely restricts the
possibility for on-line access and choosing this option may possibly create a migration problem the
next time you need to change carrier. It is not recommended that audio streams be recorded for
long term storage.
8.1.2.2 The alternative, recording a file using a computer based audio editing system and writing that file to
CD-R or DVD-R is a more reliable approach. Recording files on a 650 MB CD-R allows 59 minutes
audio storage for 48 kHz 16 bit linear PCM files, and 39 minutes for 48 kHz 24 bit linear PCM files.
Recording the same format files on a 4.7 GB DVD-R allows up to 6 hours of audio storage. For
this reason the writing of data files is recommended. Because of the simplicity and ubiquity of linear
PCM (interleaved for stereo) IASA recommends the use of a .wav or preferably the BWF .wav files
(EBU Tech 3285) if recordable CDs and DVDs are selected as the target format.
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8.1.3 Recordability, rewritability, erasability and accessibility
8.1.3.1 CD-R, DVD-R and DVD+R discs are dye-based recordable (write once) discs, but not erasable.
CD-RW, DVD-RW and DVD+RW discs are phase-change based repeatedly rewritable discs
permitting erasure of earlier data and recording of new data in the same location on the disc. DVDRAM discs are phase-change rewritable discs formatted for random access, much like a computer
hard disc.
8.1.4 Recordable CD and DVD Description
8.1.4.1 CD-Rs and DVD-/+Rs store data in line with microscopic grooves running in a spiral from the
centre of the disc to its periphery. All CD/DVD drive types use laser beams to scan these grooves.
They differ in the wavelength of the laser beam: DVDs use a narrower track pitch of 0.74μm,
compared to 1.6μm on CDs. DVD also takes advantage of new modulation and error correction
methods not available when the CD was specified.
8.1.4.2 The mechanical dimension of CDs and DVDs are equal: 120mm in diameter, and 1.2 mm thick.
The DVD, however, is made up of two discs of 0.6mm thickness, which are bonded together.
8.1.4.3 CD-R and DVD+R consist of three layers: the clear polycarbonate substrate, the dye layer and the
reflective layer. In CD-R the reflective layer is close to the label side of the disc and an additional
protective lacquer surface layer covers the fragile surface. DVD-Rs reflective layer is situated in the
middle of two polycarbonate layers. In the recording process, a laser of much higher intensity than
the reading laser “burns” the organic dye according to the coded signal, leaving a row of minuscule
transparent and non-transparent areas aligned along grooves in the disc. All recordable CDs and DVDs
contain a reflective layer that allows a reading laser to bounce off the CD/DVD and to be “read” by
the pickup sensor in the CD or DVD replay device. Many metals are suitable for use as a reflective
layer, although only two have been in widespread use on recordable CD and DVD, gold or silver. The
combination of the recorded dye groove with the reflective layer modulates the reading laser in the
same way as the injection moulded pits and lands and the reflective aluminium layer of a CD-ROM.
8.1.4.4 The three common organic dyes used in recordable discs are cyanine, phthalocyanine and azo. In
a recordable CD each dye gives the media its distinctive look depending on which metal is used
for the reflective layer; cyanine (blue) dye appears green on gold media and blue on silver media;
phthalocyanine (clear light green) dye appears transparent on gold media, but light green on silver
media; azo (deep blue) has developed into different shades of blue, the original being a deep
blue, and the more recent Super Azo a brighter shade of blue. Because the dye layer is applied so
thinly in recordable DVD the type of dye used on recordable DVDs is not easily distinguishable.
However, manufacturers of recordable CD and DVD encode information about the type of dye
in the polycarbonate layer. The CD and DVD burners use this information to calibrate laser power,
and with suitable software the information can be read by users to more accurately describe
aspects of the disc itself. This data may be read by ISRC and ATIP code viewers such as CD Media
Code Identifier (http://www.softpedia.com/get/CD-DVD-Tools/CD-DVD-Rip-Other-Tools/CDRMedia-Code-Identifier.shtml ). This tool allows users to view information such as dye type, disc
manufacturer, capacity, write speeds and media type. Clover also provides freeware device, IRSCView
(http://www.cloversystems.com/ISRCView.htm) will display the Table of Contents, Control Codes,
and ISRC codes on Audio, Mixed Mode, and Enhanced CDs. It provides much less manufacturer
information than the CD Media Code Identifier.
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Protective coating — 10µm
Reflective metal layer — 50nm
Organic dye layer — 100nm
Polycarbonate substrate layer — 1.2mm
Fig 1 Section 8.1: A schematic view of a CD-R (not to scale).
Lacquer — 10µm
Metal reflective layer — 50nm
Upper Dielectric layer — 100nm
Phase-change recording layer — 30nm
Lower Dielectric layer — 100nm
Polycarbonate substrate layer — 1.2mm
Fig 2 Section 8.1: A schematic view of a CD-RW (not to scale).
8.1.4.5 Rewritable CDs and DVDs operate on an entirely different principle. Rewritable discs are erasable
and can be rewritten, albeit a finite number of times. The recordable layer is made of germanium,
antimony and tellurium. A laser is used to heat the surface to two set temperatures. The higher
temperature is known as the melting point (approximately 600 degrees centigrade), while the
lower level temperature (approximately 350 degrees centigrade) is described as the crystallisation
temperature. Heating the disc, and controlling the cooling rate, produces a track of amorphous or
crystalline areas. Due to the different reflectivity these areas will be interpreted by the reading laser
like the pit/land structure of a CD-ROM. Earlier rewritable discs and drives could only be written at
relatively low speeds and this was encoded and implemented in the first generation of drives and
standards. More recent developments have provided a mechanism for burning data onto rewritable
discs at a higher speed. Though the older drives will read a new high speed rewritable disc, only the
latest generation of disc burners will write a disc of the latest formulation.
8.1.4.6 No trustworthy analysis of the medium or long term reliability of RW discs has been undertaken.
Preliminary investigations suggest that the film layer containing the encoded information may degrade
at a quicker rate than dye based CD-Rs (Byers 2003:9), other commentators disagree. From a purely
practical point of view, CD and DVD rewritable may present a greater risk if used for preservation
purposes as they may be overwritten by accident with a resulting loss of the original files.
8.1.5 Optical Disc Standards
8.1.5.1 Adherence to standards is the mechanism by which discs are writable or playable on different
manufacturers’ machines. The manufacturers have the responsibility to make the disc in accordance
with the particular standards. These standards, however, are not formulated with regard to longevity
or reliability of the carrier, but only format interchange. Consequently, a disc recorded and playable
on a particular machine may in fact be borderline, or even fail to meet the standard that applies.
So, although the manufacturers are responsible for the formulation of a disc, the potential life of
any information storage media will only be realised if end users take responsibility for producing
a suitable digital copy that falls within the parameters set by those standards. Relying on the
technology to meet the standards is not sufficient to ensure optimum disc life.
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8.1.5.2 This requirement to ensure that the digital information stored on an optical disc is produced in
accordance with the standards is exemplified by the issue of disc and burner compatibility. The
standards apply to the recording media rather than the replay and recording technology. Philips
warns manufacturers of disc burners that they “must implement a writing strategy giving acceptable
results”. However, this can be interpreted in a number of ways, resulting in varying compliance.
Philips/Sony attempted to address this issues with the MID (manufacturers identification code).
The nature of the production of recordable media means, however, that the only information MID
really records is the name of the manufacturer of the stampers that are used in the production of
discs. Consequently, it has done little to resolve the issue of disc/burner interaction, which remains
something of a problem.
8.1.5.3 The standards that apply to Recordable CD include Orange Book Part II: CD-R Volume 1 CD-WO
(CD write once) also known as CD-R standard describing 1x, 2x and 4x nominal CD speed. Orange
Book Part II: CD-R Volume 2: Multi-Speed CD-R (CD Recordable) describing the speeds up to 48x
nominal CD speed. Orange Book Part III: CD-RW Volume 1 CD-RW (CD Rewritable) describing
1x, 2x and 4x nominal CD speed. Orange Book Part III: CD-RW Volume 2: High Speed CD-RW
(CD Rewritable) describing 4x and 10x nominal CD speed. Orange Book Part III: CD-RW Volume
3: Ultra Speed CD-RW (CD Rewritable) describing 8x and 32x nominal CD speed. Green Book.
Compact Disc Interactive Full Functional Specification and White Book Video-CD Specification.
There are also standards for other proprietary CD formats.
8.1.5.4 The standards that apply to Recordable DVD include ISO/IEC 16824:1999 Information technology
-- 120 mm DVD rewritable disk (DVDRAM). ISO/IEC 16825:1999 Information technology—Case
for 120 mm DVD-RAM disks. ISO/IEC 17341:2004 Information technology -- 80 mm (1,46 Gbytes
per side) and 120 mm (4,70 Gbytes per side) DVD re-recordable disk (DVD+RW ). ISO/IEC
17342:2004 Information technology -- 80 mm (1,46 Gbytes per side) and 120 mm (4,70 Gbytes per
side) DVD re-recordable disk (DVD-RW). ISO/IEC 17592:2004 Information technology -- 120 mm
(4,7 Gbytes per side) and 80 mm (1,46 Gbytes per side) DVD rewritable disk (DVD-RAM). ISO/
IEC 17594:2004 Information technology—Cases for 120 mm and 80 mm DVDRAM disks. ISO/IEC
20563:2001 Information technology -- 80 mm (1,23 Gbytes per side) and 120 mm (3,95 Gbytes
per side) DVD-recordable disk (DVD-R). ISO/IEC 16969:1999 Information technology—Data
interchange on 120 mm optical disk cartridges using +RW format—Capacity: 3,0 Gbytes and 6,0
Gbytes . ISO/IEC DTR 18002 — DVD File System Specifications. ISO/IEC 13346, Recordable/
Rewritable Volume and File Structure (ECMA-167) and DVD+R - Recordable Optical Disks, 4.7 GB,
recording speed up to 4X (ECMA-349).
8.1.5.5 These standards are in addition to those specified in section 5.6.2 Standards.
8.1.6 System Description, Complexity and Cost
8.1.6.1 As noted in Chapter 2, Key Digital Principles, almost all recent generations of computers have
sufficient power to manipulate large audio files. Providing all the system standards regarding the
equipment used for conversion and ingest of audio data set out in Chapter 2 are met, the system
complexity and the degree of expertise required to run such systems is not much greater than
is necessary for desktop computer operation. Many reliable CD and DVD burning programs are
available that meet the standards required.
8.1.6.2 The only additional equipment required for the production of recordable CD or DVD is the burner,
or drive. The drives may be mounted in the computer cabinet or separate though attached to the
computer. The drives communicate with the computer through protocols such as IDE and SCSI for
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internal drives, and Firewire or USB for stand-alones. Certain drives produce lower error rate CD-Rs
and DVD-Rs than others, and it is the responsibility of staff to assess and analyse the results of the disc
burning before purchasing (see Section 8.1.9 Errors, Life Expectancy and Testing and Analysis).
8.1.6.3 The low system complexity, easy availability of technology, and inexpensive media makes the
CD-R and DVD-R a popular option with sound archives. However, as demonstrated in Chapter 6
Preservation Target Formats and Systems, the cost of a more reliable data storage system is less if
averaged across the whole collection, even for quite small collections.
8.1.7 Disc and Drive Compatibility
8.1.7.1 Compatibility between discs and drives may well be an issue when recording data on recordable
and rewritable CDs and DVDs. Situations often occur where certain discs produced on a particular
drive may produce very poor quality duplicates, or may be unreadable on other drives. Testing of this
issue has revealed that this failure rate may be very high. An International Standards Organisation
project — ISO N178 Electronic imaging — Classification and verification of information stored on optical
media, may address the specific problem of drive compatibility.
8.1.7.2 The reason for poor performance may be related to a number of factors: Early drives do not have
the laser power to calibrate on later types of discs; Drives designed for dye based discs cannot
write, and often cannot read, rewritable discs; Software issues, aging parts, particularly lasers, and
particular implementations may all produce inadequate results; The calibration information encoded
into the polycarbonate substrate may not necessarily be precisely accurate. However, even taking
these issues into account, a significant number of failures occur which are only explained as technical
incompatibilities. The equipment manufacturers’ slightly varied implementation of the disc read
standard and the variation in the discs quality mean that a situation can occur where discs and
drives are incompatible to the extent that the particular combination may produce failed discs on a
particular brand, or batch, of discs.
8.1.7.3 In order to ensure that drives and discs are compatible, it is recommended that a range of brands
of reliable and reputable discs are recorded on the selected drive, and these discs are tested to
determine error levels. This is discussed in the sections below.
8.1.8 Disc Selection.
8.1.8.1 There are three basic types of dye used on write once recordable discs, phthalocyanine, cyanine, and
azo. Manufacturers of phthalocyanine discs claim a longer life for their product than the competitors.
Some, though not all initial testing supports this view. Some manufacturers use Azo dyes in discs
that they claim are archival. Cyanine was the first dye type developed for optical disc recording, and
is generally recognised by most manufacturers as having a shorter life expectancy (LE). Dye type,
though significant, is only one of the factors determining the life of the media.
8.1.8.2 The variation in the amount of dye used in the dye layer, a result of the manufacturers’ race for
even higher recording speeds and higher density recording, is a contributing factor in the long term
failure of recordable optical media. Recording speed has increased from X1 to X52 and is still
rising, as the recording density has gone from 650MB to 800MB for CD-Rs. It should be noted that
discs optimised for high speed recording use less dye, which may indicate a shorter life expectancy.
DVD-R uses less dye as a matter of course, as the data rate when writing to a recordable DVD is
much higher than for CD-R.
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Optical discs
8.1.8.3 It is not, however, just a matter of reducing speed; if discs with a denser dye layer, optimised for
writing at lower speeds, are written at higher speeds, they deliver a worse error rate. Though
manufacturers indicate the maximum recording speed, writing at that maximum speed may not
achieve adequate results. There is an optimum writing speed at which the disc produced obtains the
best possible technical measurement for performance. Identifying this speed is best done by trial and
error measurement using a reliable disc tester. Typically, the best results will be achieved on a dense
dye layer disk written at around 8 times speed.
8.1.8.4 At best, the quality of blank recordable CD and DVD media can be described as variable. The
recordable CD and DVD- manufacturing industry has become a market place driven by narrow
profit margins and large quantities. Recordable CD and DVD manufacturing equipment has become
smaller, cheaper and more self-contained. As a consequence, the production of reliable data carriers
for the quality market has largely been replaced by manufacturers of recordable CD and DVD,
producing recordable CD and DVD for the low cost market.
8.1.8.5 Many discs that appear to be reputable brands may turn out to have been manufactured by a
second party and repackaged for sale. A recordable CD or DVD manufacturer can manipulate the
dye, reflective layer and the now expensive polycarbonate components to reduce price or control
quality. As a general rule, it has often been recommended that only reliable brand recordable CD
and DVD are purchased, however, testing has revealed a range of compliance with agreed standards
even amongst them. Instead, it is recommended that the responsible individual or institution insist on
dealing with a supplier that is open about the importer or manufacturer they deal with, and who is
able to provide contact with the relevant technical personnel in the manufacturing company. Discs
that fail the standard specified below should be returned.
8.1.8.6 It is quite difficult to identify the best quality media without high level analysers (Slattery et al., 2004).
In most practical circumstances discs must be recorded before they can be tested. Some very high
quality CD and DVD testing equipment will analyse an unrecorded disc, but most testing is carried
out by recording a test signal and analysing the result. ISO 18925:2002, AES 28-1997, or ANSI/
NAPM IT9.21 is a standard test method to establish the life expectancy of compact discs, and ISO
18927:2002/AES 38-2000 is a standard for estimating method for estimating the life expectancy
based on the effects of temperature and relative humidity for recordable compact disc systems.
As temperature and humidity aging does not always produce clear results, other approaches have
concerned themselves with the susceptibility of recordable dye based discs to light exposure with
age, and some manufacturers have undertaken testing in this area. There is, however, no standard for
this (Slattery et al., 2004).
8.1.8.7 Summary of Disc Selection
8.1.8.7.1 Purchase a range of best quality discs, based on market research.
8.1.8.7.2 Purchase more than one of each type. (Though price is not necessarily an indicator, always
remember that the cost of even the most expensive discs is small compared to the value of
the data.)
8.1.8.7.3 Under controlled conditions record some data on each of the discs.
8.1.8.7.4 Test to see which discs perform best with regard to specification in this document. All
discs must exceed the recommended quality standards recommended below (see Table 1,
Maximum error levels in an archival CDR).
8.1.8.7.5 Test at a number of different writing speeds.
8.1.8.7.6 Keep disc/burner compatibility in mind: different burners may yield different results.
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8.1.8.7.7 Choose the three best discs, from at least two dye types (phthalocyanine and azo).
8.1.8.7.8 Record identical copies of the data on the three chosen discs.
8.1.8.7.9 Ensure that delivered supplies of chosen discs are identical with tested sample discs.
8.1.8.7.10Repeat tests each time a batch of discs are purchased.
8.1.9 Errors, Life Expectancy and Testing and Analysis
8.1.9.1 The only way to know the condition of a digital collection is constant and comprehensive testing.
This cannot be stated too strongly; no collection using CD-R or DVD-R/+R as an archival carrier
should be without a reliable tester. The error correction capability of most replay equipment will
mask the effects of degradation until the errors are well into the uncorrectable region. When this
point is reached, all subsequent copies are irreversibly flawed. On the other hand, a comprehensive
testing regime allows for best possible planning of preservation strategies by acting on the known,
objective and measurable parameters that digital archiving make possible. In the well-documented
digital archive, metadata will record the history of all objects, including a record of error
measurements and any significant corrections.
8.1.9.2 Life expectancy of CD-R or recordable DVD is a many varied topic. To most end users, a CD-R or
DVD-R/+R reaches the end of its life when the drive no longer reproduces the data written on the
disc, but because drives are not governed by standards, a
CD/DVD that will not play on one drive may well play on another. There are innumerable examples
of this. The ANSI/NAPM IT9.21-1996 — Life Expectancy of Compact Discs (CD-ROM)-Method for
Estimating Based on Effects of Temperature and Relative Humidity, discusses many of these issues.
Alternately, some standards and suppliers specify an acceptable Block Error Rate (BLER). BLER is the
number of erroneous blocks per second measured at the input of the C1 decoder (see ISO/IEC
60908) during playback at the standard (x 1) data rate averaged over a 10 second measuring period.
Standards ISO/IEC 10149 and ANSI/NAPM IT9.21-1996, or Red Book standard, specify a maximum
BLER rate of 220. The standard for recording general data on CD, otherwise known as Yellow Book
standard, specify a BLER of 50. For data purposes this lower level is vital.
8.1.9.3 Studies have shown that BLER alone is not a very useful measure when determining LE, because
defective discs may exhibit BLER well under 220, or indeed under 50. It is necessary to measure
other test parameters, among them E22, E32 (uncorrectable errors), and frame burst errors (FBE,
sometimes called Burst Error Length or BERL), which are valid end-of-life indicators. When these
parameters exceed the limits specified below, it indicates a need for immediate duplication, assuming
the disc containing archival information is still readable.
8.1.9.4 Errors in archival CD-Rs should not exceed that specified in the table below. These are
maximum levels after which CD-Rs must be copied. In practice error levels much lower than
this are achievable and preferable, and must be met in order for the disc to have any archival
life before recopying becomes necessary. A BLER average of 1 and a peak level of less than
20 are easily achievable. Jitter is also a useful diagnostic indicator of the quality of the data
recorded on a CD and should be measured after writing. The 3T jitter values should not
exceed 35 nS (Fontaine and Poitevineau, 2005).
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Frame burst errors FBE
Block error rate BLER average
Block error rate BLER peak
E 22 (correctable errors)
E 32 (uncorrectable errors)
3T Jitter
<6
< 10
< 50
0
0
<35nS
Table 1 Section 8.1, Maximum error levels in an archival CD-R
8.1.9.5 The construction of a DVD is significantly different to that of the CD, and though there are many
aspects in common the criteria that applies to CDs does not necessarily apply to the DVD. Jitter
in DVDs is customarily measured in percentages. Though measured differently, the actual jitter
measurement is largely equivalent in the two disc types, the main error measurements, however,
are quite different. The two main DVD error measurements are Parity Inner Errors (PIE) and Parity
Outer Errors (POE). Industry standards state that the POE should be zero. Other types of error
measurement are defined, but at the time of writing no agreed threshold for archival purposes has
been developed. The DVD specification also states that any eight consecutive ECC blocks (PI Sum8)
may have a maximum of 280 PI errors and jitter should not exceed 9%. However, with regard to the
use of recordable CD, archival experience and testing has led to a recommendation in maximum
error levels that is approximately 25% of the red book recommendations. An extrapolation on
the DVD figures would lead to a recommendation of a maximum of 70 PI errors in any eight
consecutive ECC blocks. It is important to recognise that a distributed range of tests on DVD
recordable in archival situations has not been undertaken to assess the validity of these figures.
8.1.9.6 Initial investigations indicate that recordable CDs do not necessarily proceed to failure in a linear
way and that as a consequence small change in initial error rates could have a greater effect on
useful life of the disc. There are several tests that have indicated this to be the case (Trock, 2000),
(Bradley, 2001), however, there has not been an extended examination of this proposition.
A “longitudinal” examination of recordings over time coupled with artificial aging experiments might
bring better information on the factors of disc stability. A factor which continues to add to the lack
of consistent research is the lack of an agreed standard for the production of CD/DVD-drives.
8.1.9.7 The comparison of the solid black line to the dashed line (see Fig 1 Section 8.1 overleaf) illustrates
that the better the initial recording is the longer the expected lifetime will be. There are several tests
that have shown this to be the case (Trock JTS 2000, Bradley IASA/SEAAPAVA 2001), however,
there is no empirical proof that this is the case. The dashed line, starting at a higher error level,
decays at the same rapid rate, but starting earlier reaches failure level in a much shorter period of
time. A “longitudinal” examination of recordings with time, aging experiments, might bring better
information on the factors of disk stability. A factor adding to the lack of consistent research is the
fact that there is no standard for the production of CD/DVD-drives.
8.1.9.8 Being a composite item containing, amongst other components, organic dyes or other chemical
compounds, these optical carriers are bound to deteriorate due to slow chemical reactions.
Choosing optical discs as the target medium entails the requirement to set up a monitoring
program for the discs and a procedure for recopying discs that approach the limit of LE. The use of
recordable and rewritable CD/DVDs as archival carriers cannot be advocated unless a strict testing
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Failure threshold
Number
of errors
Time
Fig 1, section 8.1: Accumulated errors in a CD-R over time
and monitoring program is set up. It should be noted that testing and analysing, though absolutely
necessary, will be time consuming, adding long-term costs to the archival solution. When planning an
archival strategy, these costs should be included. Logs of test results should be stored, and occasional
testing, perhaps annually, can be carried out on statistically appropriate number of stored discs
carrying archival information. When the error rate is shown to be increasing, a transfer to a new
carrier can be undertaken of all the discs of that age or type.
8.1.9.9 Summary of Testing
8.1.9.9.1 Test all discs when writing.
8.1.9.9.2 Reject any discs which fail to meet specification.
8.1.9.9.3 Store the relevant test records of all discs.
8.1.9.9.4 Undertake a regular testing of a statistically significant number of stored discs of each
different batch of products.
8.1.9.9.5 Undertake a recopying of discs when error rates increase.
8.1.10 Testing of Existing Recorded Discs
8.1.10.1If data on recordable CD or DVD was not tested at the time of creation, it is critical that tests are
made of their current state. Discs must be subjected to rigorous error testing as their current error
rates play a major part in determining their further life expectancy. If error rates are measured
above the levels expressed in table 1, contents should be immediately transferred to new media.
8.1.11 Testing Equipment
8.1.11.1Professional testing equipment with dedicated, or at least specified, drives is recommended for
accurate testing DVDs and CDs. Such systems are more expensive but are necessary if accurate,
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reliable and repeatable error measurement are to be achieved. The testing should at least comply
with ISO 12142 Electronic imaging — Media error monitoring and reporting techniques for
verification of stored data on optical digital data discs. Such testing will not, however, address the
problem of the lack of standardisation of optical disc drives. There is at the moment of writing, a
standards project with the International Standards Organisation, ISO N178 Electronic imaging —
Classification and verification of information stored on optical media, which may address the specific
problem of drive compatibility. Although there is test software available on the web as shareware,
such software should be carefully evaluated before being relied on in an archival environment.
Such software based systems depend on the accuracy of the non-standard computer drives. If a
testing system based on computer drives is required, then a proprietary system supplied by the disc
manufacturer stands a better chance of being useful. At least one CD/DVD burner company does
provide software that allows their drive to be used for the purposes of testing. The results of any
testing system that depends on the CD burning drive should be checked against a known, calibrated
testing system to ensure adequate compliance.
8.1.11.2Disc test equipment which accurately measures only the parameters specified in this guidance
document are commercially available and of good standard. However, the figures provided by testing
these parameters are suitable only for identifying problems. Analysis of problems probably requires
access to a high analytical CD and DVD testing facility. It is useful to gain access to this type of
equipment, by renting or borrowing, when solving problems, selecting blank media or calibrating in
house testing facilities.
8.1.11.3Kodak, in their web-document “Permanence and Handling of CDs” (Kodak 2002) claim that 95
% of their CD-Rs will maintain a data lifetime of a hundred years in an office environment. The
results of these tests are often held to be suspect by archivists, and many have found it difficult
to reproduce the tests and achieve the same results. This may be due to different interpretation
of the figures and some argument about the validity of the method of estimating lifespan. Even
if these tests proved to be true, and in the unlikely event that CD drives are still available 100
years hence, a 5% failure rate is unacceptable in an archive. This conclusion also supports the
requirement of an error monitoring program.
8.1.11.4Accurate, High Quality Production Testers
8.1.11.4.1At the time of writing the cost of accurate, high quality production testers starts at around
US$ 30,000 for the basic models and increases to over US$ 50,000 for many devices. The
cost is incurred in the high quality reference drives which are a necessity for accurate and
repeatable testing. All testers are aimed at the market of optical disc manufacturers for
production control purposes. Actual prices depend on the scale of measurable parameters,
many of which are not relevant for testing recordable optical discs as to their archival
reliability. Currently, there are three producers of high quality testers: Audio Development
(http://www.audiodev.com/), DaTARIUS (http://www.datarius.com/) and Expert Magnetic
Corporation (http://www.expertmg.co.jp/). Manufacturers and suppliers should be
contacted for quotes.
8.1.11.5 Mid Range Quality Production Testers
8.1.11.5.1At the time of writing the cost of these devices range from a US$ 3,000 to US$ 11,000
or more. These systems test all the required parameters using standard PC drives which
have been specially selected and calibrated. It is recommended that before considering such
mid priced testers, the prospective purchaser investigate thoroughly the types of drives and
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Optical discs
the accuracy of the device. It is also strongly recommended that all mid priced systems be
regularly calibrated against a known standard. Currently, a major manufacturer of such mid
range testers is Clover Systems (http://www.cloversystems.com/)
8.1.11.6Downloadable Testers
8.1.11.6.1There are a number of downloadable testers available online which use a computer’s
inbuilt CD/DVD drive to measure error in written CD and DVDs. However, due to the
limitations of the software and inaccuracy of the drives, most, if not all, are unsuitable for
archival purposes.
8.1.12 Access and Data Migration
8.1.12.1Discrete carriers like CDs and DVDs are not well suited for on-line access. Making a collection
available necessitates staff handling the disks. Handling is one of the worst enemies of this kind
of media. Always handle the disks by the edges, and always keep them in their enclosures when
not played. The effect of light on the dyes are documented as a deteriorating factor, and excessive
temperature and humidity must be avoided, as this may hasten degradation of the disk, and in
extreme cases cause delaminating of the polycarbonate layers (Kunej 2001). The disks should be
stored in acrylic jewel cases, and cheap plastic sleeves should be avoided as they may create an
environment that is detrimental to the disk.
8.1.12.2Copying for access purposes is however an easily undertaken task, and may be done at many times
real time. There are jukeboxes on the market, which, with the appropriate software, will enable
online access to the collection, though copying to hard disc may be preferable.
8.2
Magneto-Optical Discs
8.2.1.1 The first (2004) edition of TC-04 described, as a possible target format, Magneto-Optical Discs.
By the time of publishing it had reached a capacity of 9.1 GB. This development marked the end for
this technology, and the format now has to be considered as endangered. The consequence of this is
that the media and carriers will in time become difficult, if not impossible, to obtain. All content on
M-O disc should be marked for migration to an appropriate storage system.
8.2.1.2 There has however been developed a new format that uses the same standardised 5.25 inch
caddies as the MO disks, called UDO, (Ultra Density Disc). These discs use a phase change
technology similar to CD-RW, and differ only from these in that they come in MO style caddies that
protect the discs. Some hardware systems allow for use of both MO and UDO technologies in the
same robot. A blue laser (405 nm) is used with a double-sided disc. The first UDO was presented in
fall 2003 with 30 GB storage capacity. UDO disks are currently available with a 60 GB capacity, with
a roadmap promising 120 GB in the next year, and a speculation on 500 GB as the ultimate target.
8.2.1.3 Testing and Arrhenius extrapolation have estimated a life expectancy of up to 50 years. As discussed
above in relation to other media, such testing should be considered cautiously. It is also much more
likely that format obsolescence will be the ultimate limit of long term viability. Though UDO has
some adherents, the technology has not penetrated the market to any extent and is consequently a
risk for long term archival storage.
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Optical discs
8.2.1.4 Though technological developments provide the pathway to long term preservation of our audio
content, it behoves the curator, archivist and technician responsible for an archival collection to take
a conservative and careful approach in the adoption of any new technology.
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Chapter 9: Partnerships, Project Planning and Resources
9.1.1 Introduction
9.1.1.1 The production and long term preservation of digital audio objects incorporates a number of
interrelated parts, many quite complex. These guidelines define the tasks as: Extraction of audio
content to create archival digital audio objects; Ingest of the content into a digital storage system
including the creation of necessary metadata: Administration and management of the data and
system: Archival storage: Preservation planning: and Access.
9.1.1.2 Some institutions have the facility to undertake all the tasks, as well as a collection whose size
justifies the expenditure. The alternative is to negotiate partnerships to manage some or all
of the tasks on behalf of the collection owners. These partnerships may be with other, larger
institutions, could include partnerships with like minded institutions, or could represent a commercial
relationship with a supplier.
9.1.1.3 This section of the Guidelines examines the resources required to create and preserve digital
audio objects according to technical requirements described in this document. It considers the
issues related to size of collections and scale of work, recognising that the professional fulfilment
of the requirements as described herein can only be met when the size of the collection held by
the respective institutions reaches a critical mass that make autonomous preservation viable. Many
institutions, collections or archives have particular expertise and resources in core areas which they
can deploy to facilitate the necessary processes. It is recommended that they maximise the benefit
from their core business area while carefully examining the areas where services may be better
sought elsewhere.
9.1.2 Archival Responsibilities and Collections
9.1.2.1 The first decision to be made is whether an institution should engage in digital audio preservation
at all. Often audio or audiovisual collections came about in institutions with a variety of other aims
which may not include professional preservation of audio materials. The ever increasing problems
related to the physical preservation of an audio collection, the obsolescence of dedicated replay
equipment, and digital long term preservation may suggest a rethinking of the collection and
preservation policy. Where appropriate alternatives exist, audio collections could be handed over
to more specialised institutions. This would not necessarily mean fully relinquishing ownership a
collection; the receiving archive could be asked to produce, in return, listening copies that could be
held — without significant costs — for further in-house use. Various possibilities of retaining, partly
or fully passing on the right of ownership as well as user rights could be applied.
9.1.3 Sharing archival responsibilities
9.1.3.1 Should an institution like to maintain archival responsibility for their collection a number of different
scenarios may apply which do not require relinquishing the collection.
9.1.3.2 Producing digital audio objects in-house but entrusting digital preservation to another is one
possibility. There are a number of ways this scenario could be enacted. One way, which seems
most appropriate in academic institutions and universities, is where several units are engaged in the
production and use of digital audio (and audiovisual) documents. Generally, such institutions have
a central computer facility, very often with an existing responsibility for managing various digital
objects. The data storage facility could take responsibility for the long term preservation of the
created audio content. It is important, however, that the central unit would be fully acquainted
138
Partnerships, Project Planning and Resources
with the specific of long term preservation of digital audio objects, and develops well defined rules
for the production of archival files. The central unit would prescribe recording formats, resolution,
annotation procedures, and other archival issues to be followed. Also, long term preservation tasks
of that kind could also be fulfilled by private entrepreneurs. This concept would work for newly
produced materials, specifically field recordings in various disciplines like anthropology, linguistics,
ethnomusicology, and oral history.
9.1.3.3 Another way in which this scenario might be enacted is where a large collection exists with
appropriate storage, transfer facilities and technical expertise, but where the infrastructure to
support a digital storage facility is not developed enough to build a trustworthy digital repository.
Under these circumstances the local facility may undertake the signal extraction and dispatch the
resultant digital audio objects to the selected archive.
9.1.3.4 Should institutions, however, already have accumulated, though dispersed, analogue and historical
digital originals, signal extraction from these originals to produce digital preservation files could be
concentrated in one professionally equipped unit which could also be appended to the central
computer unit. If the entire institution does not reach a critical amount of carriers, signal extraction
should better be outsourced. The same is true if the institution does not have in-house expertise or
equipment for professional digitisation.
9.1.3.5 In any of these scenarios, where a third party archive is to take responsibility for the ingest,
management and preservation of the digital audio objects, it is imperative that there is a clear
understanding of the roles and responsibilities of the various partners in the work. The ISO
20652:2006 “Data and information transfer systems -- Producer-archive interface -- Methodology
abstract standard” identifies, defines and provides structure to the relationships and interactions
between an information producer and an archive. It defines the methodology for the structure of
actions that are required from the initial time of contact between the producer and the archive until
the objects of information are received and validated by the archive. These actions cover the first
stage of the ingest process as defined in the open archival information system (OAIS) reference
model (see ISO 14721). http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.
htm?csnumber=39577
9.1.4 Critical Mass
9.1.4.1 Critical mass in the field of sound preservation is where the size of collection is sufficient to justify
the expenditure to undertake all the tasks in house. It is difficult to quote concrete numbers when
defining critical mass; the more professional institutions there are available in a country or region, the
higher the critical mass will be. If, however, there are only few institutions engaged in professional
audio archiving, or if there is none available at all, then the critical mass would be lower. Critical
mass should always relate to specific media formats; coarse grooved discs, microgroove discs, open
reel magnetic tape, etc. In fairly developed countries or regions critical mass would be at least
several thousands of items, but often institutions with tens of thousands of carriers of one type
make a rational decision to outsource signal extraction. Under less developed circumstances the
autonomous transfer of few thousand items/hours only can be carried out successfully.
9.1.4.2 The critical mass will also depend on the homogeneity of the material within the respective format.
Homogeneous collections can be transferred with some degree of automation. The cost associated
with fully automated systems generally suggests outsourcing to institutions or service providers
that offer computer controlled parallel transfers. Collections consisting of many different carriers or
standard of recording — as often found in research collections — demands reliable manual transfer,
which may be available at lower cost in house, provided the specialised expertise is available.
139
9.1.4.3 Even large, professional sound archives may consider sending parts of their collection to specialised
institutions or service providers for the purposes of transfer. This may especially be so for some
historical analogue and digital carriers.
9.1.5 Outsourcing
9.1.5.1 Whenever material is outsourced for the purpose of signal extraction, especially to private
entrepreneurs, it is important to accurately define the tasks to be fulfilled. This is best achieved by
specifying the standards provided by IASA in these Guidelines as part of the contract.
9.1.5.2 When outsourcing any audio processes it is essential to establish a quality control system that
provides a high level of assurance that all contracted work has been carried out appropriately. Such
measures should be based on stringent delivery of preservation metadata, accompanied by tests
of randomly chosen samples, including unannounced visits at service providers and testing of the
transfer equipment. Specific attention should be given to test the automated and manual quality
control systems established by the supplier, their capacity to manage long term contracts through
the use of project management methodology, experience with similar contracts and with specific
carriers, equipment maintenance, and finally the balance between cost and quality. Before the start
of the production level digitisation phase specific small tests should be performed to ensure all
aspects of the process meet criteria before commencing to process on a larger scale.
9.1.5.3 It is a responsibility of a sound archive to manage and control access to its collections in accordance
with any legal, moral or ethical constraints which are associated with the content: Outsourcing the
processes does not allow the archive to abrogate its responsibilities in this matter. When archival
material is given to a third party to undertake any audio processes it is necessary to define in
contract the restrictions under which the service provider must operate. For commercial copyright
material the legal limitations are probably described in law and can be referred to. Where privacy
or other ethical rights are of concern, these should be defined and the service provider should
acknowledge their agreement to comply. It is also important to specify how and when copies will be
eliminated from the contractor’s storage system when their responsibility comes to an end and the
material and content is returned to the owners or archive.
9.1.6 Quantitative Assessment of Project Dimensions
9.1.6.1 Whether preservation is carried out autonomously in-house, or partly or fully outsourced, an
indispensable pre-condition for seriously planning preservation is the quantitative assessment of the
project. Serious and costly mistakes are often made by underestimating the amount of work needed
for the optimal signal extraction from original carriers. Therefore, the first step is to count the
numbers of carriers and their playing time. With mechanical carriers, compact cassettes, and optical
carriers there is a fairly clear relation between the number of carriers and their respective playing
times. This may be more complex in the case of magnetic open reel collections as the playing time is
dependant on the length of the tape, the speed of recording and the numbers of tracks. However,
with good knowledge of the specific collection, some well founded assumptions can often be made
which lead to reasonably accurate estimates. In poorly documented or undocumented collections, a
situation often encountered in the estates of prominent persons, this assessment can be extremely
time consuming.
9.1.6.2 Once the duration of the carriers to be transferred is assessed, a second important factor is their
physical condition. The time factors given in the respective parts of Chapter 5, Signal Extraction from
Original Carriers, relate to well preserved items. Any cleaning and restoration measures required
may add substantially to transfer times, and must be included in the calculations accordingly.
140
9.1.7 Hierarchy of transfer to digital
9.1.7.1 Paragraph 16 of IASA-TC 03 “The Safeguarding of the Audio Heritage: Ethics, Principles and
Preservation Strategy”, describes that, except for lacquer discs, which may fail at any moment
without pre-warning, the sequence of transfer within a specific collection is a multi-faceted decision
based on the requirement for access to documents, their physical condition and, with ever increasing
importance, the availability of equipment, spare parts and professional service support. The project
“Sound Directions” has developed “FACET”1, a tool to asses the respective parameters of a
collection to assist in making a decision on a fairly objective and traceable basis. It must be noted,
however, that obsolescence of formats and related problems like withdrawal of professional service
support, e.g. for R-DAT machines, change rapidly, which calls for constant monitoring of the situation
and re-assessment in regular intervals.
9.1.8 Long term preservation of digital audio objects
9.1.8.1 It is quite common that, when commencing digital preservation, the costs of long term storage
of digital audio objects are permanently and persistently underestimated. At the time of writing
professional storage costs are considered to be in the order of a minimum of $US 5/GB/year2 for
medium to large scale storage (over 5 TB) Although the hardware cost price has been permanently
declining, the cost of the management of the storage, the continuous migration to new generation
storage, the hosting in adequate premises (clean room, etc) are always underestimated. As a political
target UNESCO has challenged the IT industry to arrive at $US 1/GB/year in the short term, a
target which seems far from being met. Some figures detailed in a PrestoSpace study show a trend
to stabilize long term storage costs at $US 9/GB/year. As digital audio objects on an average require
2 GB/hour, even future lower preservation costs will still be too high for many cultural institutions.
9.1.8.2 Lower digital storage costs can only be achieved for smaller quantities if the labour costs involved
in small scale manual approaches are not incorporated. The systematic use of open source
software may make autonomous, not fully automated processes viable in near future also for
medium amounts (10-20 TB) of storage requirements. The involvement of specialised staff to
guarantee the permanent availability of archival files in manual or semi-automatic operation must
not be underestimated.
9.1.8.3 Some service providers have recently developed adequate outsourced preservation strategies based
on the mutualisation of the use of professional large scale mass storage systems with specific access
schemes to users. Their fee is usually based on the size of the digital archives to be stored, the duration
of the contract, and the associated services. For small and medium scale archives it can be an attractive
solution, as well as for large scale archives before deciding to invest in their own storage solution.
9.1.9 Calculating overall costs
9.1.9.1 Perhaps the most crucial point when making these decisions is calculation of costs. Unfortunately,
no generally applicable concrete figures can be given in this context. In-house costs are difficult to
assess as many institutions holding audiovisual collections have infrastructures available (rooms, air
conditioning, intranet) the cost of which is incorporated into the general budget, which makes it
difficult to calculate overall costs for transfer and/or permanent digital preservation. Labour costs
differ significantly even in developed neighbouring countries, which weakens any general conclusions
1 FACET was developed within project Sound Directions by the Archive of Traditional Music, Indiana University Bloomington, USA.
< http://www.dlib.indiana.edu/projects/sounddirections/facet/>
2 Despite the current difference in monetary value USD and EURO are approximately same in the IT world.
141
as regard price. Finally, services offered by professional vendors vary considerably, depending on the
amount of items per carriers, their state of preservations and hence the possibility to automate the
process. Cost of staff, equipment and other resources generally rise over time, while it is possible
prices for some automated processes may reduce.
9.1.9.2 Because of the many factors related to a specific preservation project these guidelines refrain
from any quotation of price ranges for transfer. These guidelines suggest that holders of collections
acquaint themselves thoroughly with the specific situation in their countries or regions and observe
the market situation on a constant basis.
9.1.9.3 When seeking prices for audio preservation services, tenders must be well prepared and defined in
detail, and any subsequent offers carefully examined. Bids that offer the same service for a fraction
of other vendors should be examined with extreme scepticism. Finally, outsourcing can only be
successfully managed if a stringent quality assurance system, as described, is established, and any
substandard work is rigorously rejected.
9.1.10 Summary
9.1.10.1 In summarising preservation planning, it is strongly recommended that holders of audiovisual
collections take the present need for preserving their holdings as an occasion to rethink their overall
strategy: All scenarios, from total withdrawal from preservation responsibility, through cooperating
in or outsourcing of signal extraction and digital long-term preservation, to taking full autonomous
responsibility, should be examined. Each collection is different and institutions are embedded in a
variety of environments. These multiple scenarios, which also change over time according to technical
development, will make it difficult to decide on a purely economic basis. Generally, all holders of
audiovisual collections, specifically of small collections, are strongly encouraged to seek cooperative
relationships to manage their preservation requirements. The extent to which responsibility for signal
extraction and digital long-term preservation is accepted in-house, should be linked to the general
mission of that institution or collection. Memory institutions may decide differently from research
collections, which have a strong interest in the availability of audio documents but whose core business
does not necessarily include the processes that guarantee their further survival.
142
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Millennium JTS 2000. Paris.
Trustworthy Repositories Audit and Certification (TRAC): Criteria and Checklist http://www.crl.edu/
content.asp?l1=13&l2=58&l3=162&l4=91
Watkinson, John: 1991 R-DAT Focal Press,
Webb, Colin 2003 Guidelines for the Preservation of Digital Heritage UNESCO Memory of the World,
Internet on-line http://unesdoc.unesco.org/images/0013/001300/130071e.pdf [November 2003].
Wheatley, P. (2004) Institutional Repositories in the context of Digital Preservation. DPC Reports. Digital
Preservation Coalition.
Wright, Richard and Adrian Williams 2001 Archive Preservation and Exploitation Requirements, PRESTO-W2BBC-001218, PRESTO – Preservation Technologies for European Broadcast Archives 2001 Internet on-line,
http://presto.joanneum.ac.at/Public/D2.pdf
145
Index
A
acetate discs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
acetate tape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
ADAT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Advanced Authoring Format (AAF). . . . . . . . 15, 16
AES 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
AES 28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
AES 38. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78, 131
AES audioObject XML schema. . . . . . . . . . . . . . . 19
AES/EBU. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8, 10, 80
AES3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
AES31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 112
AES422. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
AES57. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
AIFF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
analogue magnetic tape. . . . . . . . . . . . . . 5, 7, 50, 66
acetate. . . . . . . . . . . . . . . . 32, 33, 45, 50, 62, 144
azimuth. . . . . . . . . . . . . . . . . . . . . . . . . . 56, 60, 61
binders. . . . . . . . . . . . . . . . . . . . . . . . . 50, 66, 100
cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
history . . . 44, 50, 62, 66, 82, 83, 119, 121, 132, 139
hydrolysis. . . . . . . . . . . . . . . . . . . . 50, 51, 66, 101
maintenance . . . . 5, 44, 52, 57, 63, 68, 85, 86, 92,
102, 104, 106, 107, 118, 140
noise reduction. . . . . . . . . . . . . . . . 41, 59, 60, 63
print-through. . . . . . . . . . . . . . . . . . . . . . . . 61, 62
PVC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45, 50, 62
selection of best copy. . . . . . . . . . . . . . . 5, 33, 45
wow and flutter. . . . . . . . . . . . . . . . 38, 56, 57, 61
audio specific data storage
CD-DA. . . . . . . . . . . . . . . . . . . . . . 74, 76, 90, 126
DAT . . . . . 5, 7, 67–69, 72, 90, 101, 121, 141, 145
autoloader. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
coarse groove discs . . . . . . . . . . . . . . . . . . 34, 46
cylinders. . . . . . . . . . . . . . . . . . . . . . . . . . . . 34, 46
LP recordings. . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Magnetic digital tape. . . . . . . . . . . . . . . . . . . . . 66
CD family. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Cetrimide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
cleaning. . . . . . . . . 5, 34, 35, 46, 51, 57, 66, 67, 78, 79,
85, 140, 144
analogue magnetic tape. . . . . . . . . . . . . . . . . . 51
CD and DVD . . . . . . . . . . . . . . . . . . . . . . . . . . 78
coarse groove discs . . . . . . . . . . . . . . . . . . . . 5, 7
instantaneous discs. . . . . . . . . . . . . . . . . . . 32, 33
LP records. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 7
magnetic digital carriers. . . . . . . . . . . . . . . . . . 66
record cleaning machines. . . . . . . . . . . . . . 34, 46
ultrasound. . . . . . . . . . . . . . . . . . . . . . . . . . 35, 46
COA (Contextual Ontology Architecture). . . . . 16
coarse groove discs (78 rpm). . . . . . 5, 7, 33, 39, 42,
43, 45, 78, 139, 144, 145
coercivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61, 73
Compact cassette. . . . 5, 7, 50, 51, 55–57, 59–61, 63,
66–69, 73, 101, 140, 144
computers.10, 14, 18, 26, 100, 105, 108, 109, 124, 129
Contextual Ontology Architecture. . . . . . . . . . . . 16
cylinder phonographs
specification. . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
cylinders. . . . . . . . . . . . . . . . 32, 34, 35, 37, 38, 39, 43
D
calibration disc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
carrier restoration. . . . . . . . . . . . 5, 34, 45, 51, 66, 78
analogue magnetic tape. . . . . . . . . . . . . . . 51, 66
CD and DVD . . . . . . . . . . . . . . . . . . . . . . . . . . 78
DASH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69, 70
DASH (Digital Audio Stationary Head)
See also magnetic digital carriers. . . . . . . . . . . 69, 70
DAT . . . . . 5, 7, 67, 68, 69, 72, 90, 101, 121, 141, 145
DAT (Digital Audio Tape ) See also magnetic digital
carriers. . . 5, 7, 67, 68, 69, 72, 90, 101, 121, 141, 145
data reduction. . . . . . . . . . . . . . . . . . . . . . . 11, 81, 82
data tape . . . . . 5, 100, 101, 102, 103, 104, 105, 109,
. . . . . . . . . . . . . . . . . . . . . . . . 118, 122, 123, 124, 125
data tape formats. . . . . . . . . . . . . . . . . . . . . 100, 102
AIT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
autoloaders. . . . . . . . . . . . . . . . . . . . . . . . . . . 103
backup. . . . 87, 99, 102, 103, 104, 106, 110, 111,
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122, 124, 125
costs. . . . 14, 21, 26, 44, 102, 104, 105, 106, 107,
. . . . . . . . . . . . . . . . . 108, 110, 125, 134, 138, 141
DLT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
DTF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
HSM. . . . . . . . . . . . . 100, 103, 104, 106, 110, 122
LTO. . . . . . . . . . . . . . . . . . 101, 104, 106, 111, 123
146
B
backup . . . . . 84, 86, 87, 99, 102–104, 106, 110, 111,
122–124, 125
BEXT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12, 19, 121
bias. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
binders, tape. . . . . . . . . . . . . . . . . . . . . 50–52, 66, 100
bit depth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 8, 11
Broadcast Wave Format (BWF). . . . . . 4, 12–14, 18,
28, 74, 80, 82–84, 90, 97, 98, 112, 121, 122, 126
C
Index
robotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
table of formats. . . . . . . . . . . . . . . . . . . . . . . . 102
tape coatings. . . . . . . . . . . . . . . . . . . . . . . . . . 100
data vs audio specific storage. . . . . . . . . . . . . . . . 77
dbx. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18, 20–27
DC 15 elements. . . . . . . . . . . . . . . . . . . . . . . . . . . 22
DC Terms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22, 23
DCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
DCMI. . . . . . . . . . . . . . . . . . . . . . . . 17, 19, 20, 24–27
dictation machines. . . . . . . . . . . . . 5, 7, 32, 43, 62, 63
Dictabelt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Dictaphone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Digital Compact Cassette (DCC) See also magnetic
digital carriers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Digital Mass Storage System (DMSS). 5, 90, 99, 100,
118, 124
Digital Mass Storage Systems (DMSS) Principles.90
digital tape. . . . . . . . . . . . . . . . . . . . . . . 65, 66, 67, 73
disc flattening. . . . . . . . . . . . . . . . . . . . . . . 36, 46, 144
Dolby. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59, 60
DSD See Super Audio CD (SACD). . . . . . . . . . . 81
DTD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17, 18
Dublin Core. . . . . . . 16, 17, 18, 21–24, 120, 121, 143
Dublin Core Metadata Initiative . . . . . . . . . . . 17, 24
DVD.5, 7, 74–82, 88, 90, 118, 126–133, 134–136, 143
replay See optical disk replay. . . . . . . . . . . . . . 79
DVD audio. . . . . . . . . . . . . . . . . . . . . . . . . . 74, 76, 80
E
equalisation . . . . . 5, 32, 38, 39, 40, 41, 47, 48, 56, 57,
58, 59, 60, 63
78 rpm discs . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
coarse groove electrics. . . . . . . . . . . . . . . . . . . 40
coarse groove standards. . . . . . . . . . . . . . . . . 40
flat (definition) footnote . . . . . . . . . . . . . . . . . 41
LP records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
equalization
chart. . . . . . . . . . . . . . . . . . . . . . . . . 42, 45, 47, 49
error measurement
CD-R and DVD. . . . . . . . . . . . .67, 131, 133, 135
DAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Extensible Markup Language (see also XML). . . 16
F
field recording. . . . . . 2, 19, 52, 65, 69, 83, 84, 86, 87,
88, 89, 90, 139
AB parallel pair. . . . . . . . . . . . . . . . . . . . . . 86, 87
ATRAC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81, 83
microphones. . . . . . . . . 32, 42, 84, 85, 86, 87, 88
MP3 . . . . . . . . . . . . . . . . 10, 13, 83, 109, 116, 124
MS (Mid-Side). . . . . . . . . . . . . . . . . . . . . . . 86, 87
selection of field recording equipment. . . . . . 84
testing and maintenance. . . . . . . . . . . . . . . . . . 85
XY crossed pair. . . . . . . . . . . . . . . . . . . . . . 86, 87
Field Recording Standards. . . . . . . . . . . . . . . . . . . 83
file formats. . . . . . . . . . . . . . . . . 10, 11, 12, 19, 90, 92
flat copy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
format obsolescence. . . . . . . . . . . . . . . . . . . 101, 137
Functional Requirements for Bibliographic Records
(FRBR) . . . . . . . . . . . . . . . . . . . . . . . . . . 16–17, 21, 27
G
gelatine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33, 34
H
hard disc drives.74, 101, 105–110, 118, 122–127, 136
cost. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
disk only storage. . . . . . . . . . . . . . . . . . . . . . . 105
Firewire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
life. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
RAID. . . . . . . . . . . . . . . . . 105, 106, 108, 123, 124
reliability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
SATA/ATA. . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
SCSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
USB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Hierarchical Storage Management (HSM). . . . . 100,
103, 104, 106, 110–111, 122
hill-and-dale See also vertical cut disc. . . . . . . . . . 32
historical and obsolete mechanical formats. . . . . 32
acetate discs. . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34, 46
coarse groove records. . . . . . . . . . . . . . . . . . . 32
equalisation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
replay equipment . . . . . . . . . . . . . . . . . . . . . . . 36
replay speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
restoration. . . . . . . . . . . . . . . . . . . . . . . . . . 34, 46
selection of best copy. . . . . . . . . . . . . . . . . . . . 32
tracking force. . . . . . . . . . . . . . . . . . . . . . . . 37, 39
hydrolysis. . . . . . . . . . . . . . . . . . . . . . . 50, 51, 66, 101
treatment of tapes . . . . . . . . . . . . . . . . . . . 51, 66
I
IASA-TC 03. . . . . . . . . . . . . . . . 2, 4, 5, 115, 141, 144
ID3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
instantaneous disc. . . . . . . . . . . . . . . . . . . . 32, 33, 36
Issues with DVD Audio . . . . . . . . . . . . . . . . . . . . . 80
147
Index
J
JHOVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19, 97
jitter. . . . . . . . . . . . . . . . . . . . . . . . . . . . 9, 10, 132, 133
JSTOR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19, 97
L
lacquer disc . . . . . . . . . . . . . . . . . . . . 32–37, 127, 141
lateral cut discs . . . . . . . . . . . . . . . . 32, 33, 36, 37, 45
lifespan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6, 135
LP records. . . . . . . . . . . . . . . . . . . . . . 5, 7, 32, 45–49
cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
replay equalisation. . . . . . . . . . . . . . . . . . . . . . . 48
replay equipment . . . . . . . . . . . . . . . . . . . . . . . 47
M
magnetic digital carriers. . . . . . . . . . 5, 65, 66, 67, 90
cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
DASH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69, 70
DAT . . 5, 7, 67, 68, 69, 72, 90, 101, 121, 141, 145
DCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Minidisc. . . . . . . . . . . . . . . . . . . . . . . . . . 81, 82, 84
Pro-Digi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
replay equipment.5, 6, 11, 37, 43, 44, 48, 50, 57, 61,
62, 63, 72, 73, 77, 80, 82, 132, 143
selection of best copy. . . . . . . . . . . . . . . . . . . . 65
video tape formats. . . . . . . . . . . 5, 7, 65, 73, 100
magneto optical (MO) disks . . . . . . . . . . . . . . 5, 137
MARC. . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 23, 24, 144
Material Exchange Format (MXF). . . . . . . 11, 16, 97
MD see Minidisc. . . . . . . . . . . . . . . . . . . . . 19, 81, 82
metadata. . . . . . .2, 4, 5, 11, 12–27, 28, 29, 38, 39, 41,
44, 63, 65, 67, 69, 73, 76, 77, 79, 80, 83, 88, 89, 91–99,
103, 112, 116, 117, 119, 121, 122, 132, 138
BEXT . . . . . . . . . . . . . . . . . . . . . . . . . . 12, 19, 121
COA (Contextual Ontology Architecture). . 16
DC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18, 21–25
DC 15 elements. . . . . . . . . . . . . . . . . . . . . . . . 22
DC Terms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
DCMI. . . . . . . . . . . . . . . . . . . . . . . . 17, 22–25, 27
DTD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17, 18
Dublin Core.16, 17, 18, 21, 22, 24, 120, 121, 143
Dublin Core Metadata Initiative . . . . . . . . 17, 24
Extensible Markup Language see XML. . . . . . 16
FRBR (Functional Requirements for Bibliographic
Records). . . . . . . . . . . . . . . . . . . . . . 16–17, 21, 27
ID3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
MARC . . . . . . . . . . . . . . . . . . . . 16, 23, 24, 25,144
Material Exchange Format metadata (MXF). . . 11,
16, 97
METS (Metadata Encoding and Transmission
Standard). . . 13, 14, 18–21, 24, 97, 99, 119, 121
MODS. . . . . . . . . . . . . . . . 16, 18, 21, 24, 25, 144
MP3 . . . . . . . . . . . . . . . . 10, 13, 83, 109, 116, 124
MPEG-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 16
OAI-PMH (Open Archives Initiative Protocol for
Metadata Harvesting). . . . . . . . 16, 24, 117, 144
ontologies . . . . . . . . . . . . . . . . . . . . . 2, 16, 17, 27
OWL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
PREMIS. . . . . . . . . . . . 12, 17, 19, 26, 82, 112, 145
preservation metadata.5, 17, 18–19, 88, 112, 140
RDF. . . . . . . . . . . . . . . . . 17, 18, 21, 23, 24, 25, 28
SMPTE. . . . . . . . . . . . . . . . . . . . 9, 16, 68, 97, 144
XML. . . 15, 18, 19, 21, 26, 88, 97, 114, 116, 121
metal stampers. . . . . . . . . . . . . . . . . . . . . . . . . 37, 38
replay of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
METS (Metadata Encoding and Transmission
Standard) . . . . . . . 13, 14, 18–21, 24, 97, 99, 119, 121
microphones. . . . . . . . . . . . 32, 42, 84, 85, 86, 87, 88
MIDI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7, 57, 76
Minidisc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81, 82, 84
MODS. . . . . . . . . . . . . . . . . . . 16, 18, 21, 24, 25, 144
MP3. . . . . . . . . . . . . . . . . . . . 10, 13, 83, 109, 116, 124
MPEG-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 16
Mylar see also polyester tape. . . . . . . . . . . . . . 50, 60
N
Nagra-D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69, 70
Network Attached Storage (NAS). . . 108, 110, 124
O
OAI-PMH (Open Archives Initiative Protocol for
Metadata Harvesting). . . . . . . . . . . . 16, 24, 117, 144
OAIS (Reference Model for an Open Archival
Information System). . . 2, 27, 93–99, 110, 112, 114,
115, 118, 119, 120, 122, 139
ontologies. . . . . . . . . . . . . . . . . . . . . . . . . 2, 16, 17, 27
optical disk. . . . . . . . . . . . . . . . . . . . . . . 5, 7, 126, 129
optical disk recording
CD failure rates. . . . . . . . . . . . . . . . . . . . . . . . 134
CD testing. . . . . . . . . . . . . . . . . . . . . . . . 130, 132
CD-Recordable. . . . . . . . . . 74, 76, 77, 78, 79, 90,
126–137, 143, 144, 145
costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
DVD-Recordable . . . . . . . . . 74, 76, 79, 126–137
dyes. . . . . . . . . . . . . . . 74, 127, 128, 130, 131, 132
error measurement . . . . . . . . . 67, 131, 133, 135
148
Index
error recommendations. . . . . . . . . . . . . 131, 133
introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
life. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
life expectancy. . . . . . . . . . . . . . . . . . . . . 130, 132
recording formats. . 32, 43, 73, 81, 83, 84, 90, 139
Red Book. . . . . . . . . . . . . . . . . . . . . . . . . . 76, 132
Yellow Book. . . . . . . . . . . . . . . . . . . . . . . . 76, 132
optical disk replay
CD family. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
selection of best copy. . . . . . . . . . . . . . . . . . 5, 33
Super Audio CD (SACD). . . . . . . . . . . . . . . . 81
time factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
optical replay. . . . . . . . . . . . . . . . . . . . . . . . . . . 36, 40
coarse groove recordings. . . . . . . . . . . 36, 38, 40
LP records. . . . . . . . . . . . . . . . . . . . . . . . . . 38, 47
OWL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
replay equipment
analogue cassette. . . . . . . . . . . . . . . . . . . . . . . 56
analogue reel tape. . . . . . . . . . . . . . . . . . . . . . . 52
coarse groove discs . . . . . . . . . . . . . . . . . . . . . 36
DVD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
LP records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
replay speed. . . . . . . . . . . . . . . . . . . . . . . . . 38, 57, 63
capstan-less machines. . . . . . . . . . . . . . . . . . . . 57
cassette. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
cylinders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
LP records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
reel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
restoration see also carrier restoration . . . . . . . . . 5
P
sampling rate. . . . . . . . . 8, 11, 13, 14, 17, 71, 83, 121
SCSI. . . . . . . . . . . . . . . . . . . . 104, 105, 109, 129, 143
selection of best copy. . . . . . . . . . . . . . . . . . . . . 5, 33
CD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
coarse groove records (78 rpm) . . . . . . . 32, 45
cylinders. . . . . . . . . . . . . . . . . . . . . . . . . . . . 32, 45
DVD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
instantaneous discs. . . . . . . . . . . . . . . . . . . . . . 33
LP records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
selection of field recording equipment. . . . . . . . . 84
signal extraction. . 1, 2, 4, 5, 6, 31, 65, 67, 76, 83, 139,
140, 142
Small Scale Approaches to Digital Storage
Systems. . . . . . . . . . . . . . . . . . . . 1, 2, 11, 13, 118–125
archival storage. . . . . . . . . . . . . . . . . . . . 105, 122
basic metadata. . . . . . . . . . . . . . . . . . . . . . 12, 121
configuration. . . . . . . . . . . . . . . . . . . . . . . . . . 118
description of system. . . . . . . . . . . . . . . . . . . 119
hardware. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
partnerships and backup. . . . . . . . . . . . . . . . 125
preservation planning. . . . . . . . . . . . . . . . . . . 122
repository software . . . . . . . . . . . . . . . . . . . . 120
risks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
SMPTE. . . . . . . . . . . . . . . . . . . . . . . 9, 16, 68, 97, 144
sound cards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Sources of Metadata. . . . . . . . . . . . . . . . . . . . . 26–27
speed
capstan-less machines. . . . . . . . . . . . . . . . . . . . 57
cassette. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
persistent identifier. . . . . . . . . . . . . . . . . . . . . . . . . 28
phthalocyanine see also optical disk recording. . . 127,
130, 132
piano rolls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
polyester tape. . . . . . . . . . . . . . . . . . . . . . . 50, 62, 66
PREMIS. . . . . . . . . . . . . . . 12, 17, 19, 26, 82, 112, 145
preservation
aim of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
digital. . . . . . . 2, 4, 6, 8, 9, 20, 65, 90, 91, 112, 114,
118, 126, 138, 139, 141, 144
preservation metadata. . 5, 17, 18, 19, 26, 88, 112, 140
PRESTO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50, 145
print-through. . . . . . . . . . . . . . . . . . . . . . . . . . . 61, 62
Pro-Digi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Pro-Digi see also magnetic digital carriers. . . . . . 70
PVC tape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50, 62
Q
quantisation. . . . . . . . . . . . . . . . . . . . . . . . . 10, 65, 76
quarter track heads. . . . . . . . . . . . . . . . . . . . . . . . . 54
R
radio transcription discs. . . . . . . . . . . . . . . . . . 32, 37
RAID (Redundant Array of Inexpensive (or
Independent) Disks). . . . . . . 105, 106, 108, 123, 124
R-DAT see also magnetic digital carriers . . . 5, 7, 67,
68, 69, 72, 90, 101, 121, 141, 145
RDF. . . . . . . . . . . . . . . . . . . . 17, 18, 21, 23, 24, 25, 28
Red Book. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76, 132
reel tape see also analogue magnetic tape. . . . . 5, 7,
50, 52, 56, 57, 59, 61, 62, 63, 66, 69, 73, 139, 140
S
149
Index
cylinders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
LP records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
reel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
speed see also replay speed. . . . . . . . . . . . 38, 57, 63
standards . . . . . . 2, 3, 4, 5, 8, 9, 11, 13, 15, 16, 17, 21,
24, 25, 26, 27, 32, 39, 43, 45, 48, 53, 55, 56, 58, 59, 61,
65, 66, 71, 72, 76, 77, 80, 83, 88, 92, 97, 104, 112, 114,
117, 118, 120, 128, 129, 131, 132, 133, 135, 140, 144
analogue tape . . . . . . . . . . . . . . . . . . . . . . . 55, 58
analogue tape heads. . . . . . . . . . . . . . . . . . 53, 54
CD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76, 129
coarse groove recordings (78 RPM). . . . . . . . 43
cylinders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
digital audio cassette. . . . . . . . . . . . . . . . . . . . . 69
digital reel formats . . . . . . . . . . . . . . . . . . . . . . 69
DVD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76, 129
field recording. . . . . . . . . . . . . . . . . . . . . . . . . . 83
LP recordings. . . . . . . . . . . . . . . . . . . . . . . . . . . 48
magnetic digital tape. . . . . . . . . . . . . . . . . . . . . 66
RIAA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
sound cards. . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
storage formats see also target formats. . . . . . 5, 83
styli. . . . . . . . . . . . . . . . . . . . . . . 33, 36, 38, 41, 47, 48
coarse groove records. . . . . . . . . . . . . . . . . . . 36
cylinder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
LP records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Super Audio CD (SACD) . . . . . . . . . . . . . . . . . . . 81
issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
survey of endangered carriers. . . . . . . . . . . . . . . . 50
U
U-Matic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
UNESCO. . . . . . . . . . . . . . . . . . . . . 90, 141, 143, 145
V
vertical cut recording. . . . . . . . . . . . . . . . . . . . 32, 37
video soundtrack. . . . . . . . . . . . . . . . . . . . . . . . . . . 11
video tape based audio formats. . . . . . . . . . . . . . 70
video tapes. . . . . . . . . . . . . . . 5, 7, 65, 66, 70, 73, 100
videocassettes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
vinyl records see also LP records. . . . 5, 7, 33, 36, 45,
46, 47, 144
W
wav (Wave). . . . . . 4, 9, 11, 12, 18, 19, 28, 32, 74, 80,
81, 83, 84, 90, 97, 98, 112, 126
wax cylinders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
web. . . . . . . . 15, 16, 24, 27, 28, 76, 96, 116, 117, 120,
135, 143, 144
Web 2.0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
wire recordings. . . . . . . . . . . . . . . . . 5, 7, 62, 63, 124
wordclock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
X
XACML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
XML. . . . . . . 15, 18, 19, 21, 26, 88, 97, 114, 116, 121
Z
Z39.50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26, 116
Z39.85- NISOZ3985. . . . . . . . . . . . . . . . . . . . . . . 21
T
tape
digital. . . . . . . . . . . . . . . . . . . . . . . . . 65, 66, 67, 73
tape libraries (data). . . . . . . . . . . . . . . . 102, 103, 104
tape speeds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
tape see also analogue magnetic tape
analogue. . . . . . . . . . . . . 50, 52, 58, 61, 63, 67, 73
target formats. . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
archival storage. . . . . . . . . . . . . . . . . . . . . 99, 112
CD-R and DVD-R. . . . . . . . . . . . . . . . . . . . . . 130
TelCom. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
test disc see also calibration disc. . . . . . . . 38, 43, 47
test record see also calibration disc . . . . 47, 48, 135
testing and maintenance (field recording). . . . . . 85
tracking, digital tape. . . . . . . . . . . . . . . . . . . 68, 72, 79
tracking, disc. . . . . . . . . . . . . . . . . . . . . . 37, 38, 39, 47
turntable
specification. . . . . . . . . . . . . . . . . . . . . . . . . 37, 48
turntables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
150
Asociacion
Technical Committee
Audio Objects
IASA-TC04
Second Edition
IASA-TC04 Second Edition
http://www.iasa-web.org
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Guidelines on the Production and Preservation of Digital Audio

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