How Loud is a Movie? – a New Measurement

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HowLoudisaMovie?–aNewMeasurementProcedure
ByIoanAllen
This advance release of the paper has been released as a courtesy to interested
members of the ISDCF.
Accepted for publication and copyright SMPTE - reproduced by permission. Ioan Allen Author.
ISDCF-Doc11 Movie Loudness Measurement 20160315
Leq(m10)2.0
HowLoudisaMovie?–aNewMeasurementProcedure
ByIoanAllen
Abstract:
Aprocedureisintroducedtomeasurethesubjec;veloudnessofanen;removieandto
developasuitablemetric.Leq(m)hasbeenusedforover15yearstomeasureandthencontrol
theleveloftrailersandcommercials,bothintheUSandoverseas.Themethodtobedescribed
takesaten-minuterollingaverageofLeq(m)throughoutanen;removie,andthenintegrates
thevaluesaboveagiventhreshold.Theprocedureisnotintendedtoconstrainthelevelsof
movies,simplytocomeupwithametrictodescribethesubjec;veloudness.Asuggested
descrip;veisLeq(m10).
History:
Asthesoundqualityof35mmfilmimprovedovertheyears,fromAcademymono,through
DolbyStereo,DolbySR,andthedigitalsoundon35mmfilmformats,sodidthepeaklevel
achievableoneachchannelofasoundtrack.
Figure1.PeakLevelCapabilityofPhotographicSoundtrackFormats
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Andeachdevelopmentalsoincreasedthechannelcount,furtherraisingthepoten;almaximum
soundpressurelevelinthecinema.
Nowthemoviebusinessisuniqueinmanyways!Andoneoftheseisthepoten'alforcontrol
ofimageandsoundqualitythroughoutthechainfromstudiotoexhibi;on.Incontrast,the
producerofaradioprogramortelevisionshowhasnocontrolwhatsoeverovertheconsumer’s
playbackcoloradjustment,ortheseVngofthevolumecontrol.Weusedtheword“poten;al”
becausethetheatreoperatorcanalwaysover-ridethereferenceseVngsofsoundandpicture.
Acorrectlyalignedtheatreplayingamovieatfader7willreproducethelevelheardbythe
directorandmixeronthedubbing/mixingstage.Excessiveuseofthepowercapabili;esof
contenttechnology,though,leadstomanyatheatrefaderbeingloweredfromreference7to6,
5oreven4½,areduc;onofasmuchas10dB.Needlesstosay,suchaloweringoflevelleadsto
severedialogintelligibilityproblems.
Now,afilm’sdirectormayhaveul;matecontrolofthefilmitself–buttrailersareinpart
controlledbythestudios’marke;ngdepartment.Inevitably,thetrailerdesignersfeelthatthey
areincompe;;onwithothertrailers,andwillpackeveryavailablehighlightfromthetwo-hour
movieintothe90secondtrailer.Naturally,thehighlightsmoreocenthannotwillbethe
loudestelements.
Digitalsoundon35mmfilmwasintroducedin1992–andtheloudnesswarsbetweentrailers
becamesoviolentthatthereweremanycomplaintsfromtheatreownersandthegeneral
public,highlightedbytrailersforfilmssuchasTwister(1996),StarWars(1997–re-release)and
MeninBlack(1997).Astheatrechainsemployedfewerprojec;onists,andmanycinemaswere
notequippedwithautoma;oncontroloffaderseVngs,aloweredplaybacklevelofthetrailers
ledtothesamereducedlevelbeingappliedtothefeature.Asaresult,therewereincreased
complaintsofinaudibledialoglevelsonfeaturefilms–notsurprisingwhenthedialoglevelshad
beenloweredbyasmuchas10dBbelowreference!
Thestudiosrealizedthatthingswereoutofcontrol,andacommieee,laterknownasTASA,was
formedbythe(then)sevenmajorstudiostoreviewthesitua;on.
Leq(m):
Foryearsaprocesshadbeenu;lizedtomeasuretheaveragesoundleveloftypicallyindustrial
noiseover;me,referredtoasLeq.Thisaveragingmethodcommonlyu;lizesa“weigh;ng”
characteris;c,whichhighlightscertainfrequenciesdependingontheapplica;on.Seebelow,
andFigure2.DolbyLaboratoriescarriedoutsomeresearchworkin1996todeterminetheideal
weigh;ngcharacteris;cforthemeasurementoftrailersandcommercials,bothofwhich
typicallyhaveaforcefuluppermid-frequencydominance.
ThisledtotheirproposalforameasurementprocedurecalledLeq(m),with“m”standingfor
“movies”.(1)
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Hierarchy:
Theinten;onofaloudnessmeasurementsystem,notsurprisingly,istogetaseriesofnumbers
whichmatchthesubjec;veloudness.Inotherwords,ifsampleAissubjec;velylouderthan
sampleB,andsampleBlouderthanC,thenthemeasurementsystemshouldalsoshowthat
A>B>C.Inthiscontext,thescaleA>B>Ccanbereferredtoasa“hierarchy.”
Therearenumerousweigh;ngcurvesinusefordifferentapplica;ons.Mostcommonis
probablyA-weigh;ng,typicallyusedtomeasuretheannoyancefromindustrialnoise.Itwas
foundwhenevalua;nganumberoftrailersandcinemaspecificcommercialsthattheMweigh;ngcurve,favoringthe2kHzto3kHzregions,createdabeeer“hierarchy”thanCweigh;ng,A-weigh;ngandnoweigh;ngatall.SeeFigure2.
Figure2:M-Weigh;ngcurve
TASA:
TASA(theTrailerAudioStandardsAssocia;on)haditsfirstmee;nginAugust1997.The
inten;onwastomeasureandcontroltheleveloftrailers.Theassocia;onadoptedLeq(m)as
themeasurementprocedure,andtoformalizecontrolprocedure;edtheTASAprogramwith
thera;ngsprocedureoftheMPAA.InJune1999theMPAAadministra;onformallybegan,and
sincethatdatenoapprovalra;nghasbeengiventoanytrailerwithoutTASAcer;fica;on.An
ini;almaximumlevelwas87dBLeq(m),andthiswasloweredintwostepsto85dBLeq(m)in
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2001,andremainstheretodayforbothfilmanddigitalcinema.Comparethiswith1996and
1997whentheloudesttrailersmeasured92and93dBLeq(m).Thismeansthattheloudest
trailerstodayare8dBquieterthanbeforeTASAwasintroduced.Italsomeantthatthetrailers
beeermatchedthelevelofthefeatures.
Over6000trailersforUSfeatureshavenow(2015)passedthroughtheTASAapprovalrou;ne.
Theprocesshasbeenadoptedbyseveralna;onalstandardsbodies,andbytheInterna;onal
StandardsOrganiza;on.(2)
PotenIallegislaIon:
“It’sthesqueakywheelthatgetstheoil.”Surveysandcinemaexitpollssuggestthatmost
movie-goersarecontentwiththevolumelevelsofcommercials,currenttrailersandthe
features.Butthecomplaintsthatdoarrivefrequentlygetwidelyreportedinthepress–where
thear;cleswillrarely,ifever,pointoutthatthemovie-goingexperienceisfarquieterthanthe
sustainedloudnessofafootballgame,orevenahigh-schoolbasketballgame.
From;me-to-;mepoli;cianshavereactedtothesepressar;clesbythreateninglegisla;on.
Butunfortunatelysomeofthepoten;allegisla;onhassuggestedconstrainingthepeaklevel
heardinthecinema.Thiswouldbewrongfromtwostandpoints.First,itputstheonusonthe
theatreownertocheckandcontrolthelevels–asmen;onedpreviously,withacorrectly
alignedtheatre,thelevelsaresetbythefilm-maker.Secondly,controlofpeaklevelscouldwell
constrainthear;s;cintentofthefilm-maker–asinglegun-shotatpeaklevelsurprises,but10
minutesofsustainedmachine-gunfirewouldproveextremelyannoying!
Luckily,atleastintheUS,nothreatenedlegisla;onhassofarbeenenacted.
Whatistheloudnessofafeaturefilm?
Theauthorisfirmlyagainstanyconstraintoflevelsoffeaturesfilms,believingthattobethe
domainofthefilm’sdirectorandsoundcrew.Ifthefilm-makersarefoolhardyenoughtooverabusethetechnologybypilinguptheloudness,that’suptothem.
Butthatsaid,thereisonemissinglink–thereisnoestablishedmethodofdeterminingthe
subjec;veloudnessofanen;refeaturefilm.IthasbeensuggestedthatanLeq(longterm
average),suchasLeq(m),couldbeused.Thisdoesn’twork–thinkofafilmhaving6twentyminutereels.Imaginereels1-5beingveryquiet,butthewholeofreel6beingat100%peak
level.AnLeqreadingwouldcomeoutquitelow,buttheaudiencewouldcomeoutscreaming
attheendofreel6.Twentyminutesat100%isobviouslytoomuchsustainedloudness.
So,atanyonepointin;me,let’sconsidertheideaofmeasuringtheLeqoftheprior(let’ssay)
10minutes.(SeeFigure3)
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Figure3:Notthecurrentvalue,butanaverageoftheprevioustenminutes
Thiswouldbeausefulstar;ngtool–theLeqmeasurementwouldnotbeundulyinfluencedby
afewsuddenpeaks,butwouldclearlyshowupprolongeduseof100%capability.
Andbecausewe’retryingtoassesstypicalfilmprogrammaterialhere,applyingthesameMweigh;ngasisbeingusedforthesubjec;vemeasurementoftrailers,thisten-minuteaverage
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wouldbeweightedinthesameway–let’scallitLeq(m10).Hereareafewexamples
Figure4:StarWarsEpisodeII
Figure5:MasterandCommander
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Figure6:MissionImpossible3
Figure7:VeerZara
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Ametric:
Butthisinitselfisnotveryuseful.It’snotveryhelpful,forexample,justtosaythatat23
minutesintothefilm,theLeq(m10)fortheprevioustenminuteswas85dB,ortostateitmore
correctly,85dBLeq(m10).
So,let’stryaddingtogetheralltheLeq(m10)readingsatsomegivenconstantclockfrequency
(samplerate),andthendividingbythedura;onofthefilm.
Forthefirsttenminutesofthemovie,thedatawillshowaconven;onalLeqreading.Atthe
ten-minutepoint,thepre-tenminutesampleswillbedroppedoff.Thelastreadingwillbetaken
atLFOA.
Tomakeafurtherimprovement,wedon’twanttohavetheresultinfluencedinanywayby
sustainedlow-levelmaterial.Asanexample,thedifferencebetweenquietdialogandquiet
atmospheresshouldhaveminimaleffect.Ourinterestisonlyinsustainedmaterialabovea
certainlevel.So,let’ssetathresholdpoint.
Ourstar;ngparameterswere:
1. Windowdura;on–currently10minutes
2. Threshold–ini;ally85dBLeq(m10),butchangedlater(seebelow)
3. Samplerate–currently750mS-nota;meconstant,butthepointatwhichasampleis
taken.
4. Filmdura;onunits–minutes(whynot?)
Abunchoffilmsweremeasuredusingtheseparameters,crea;ngasinglemetric,anda
hierarchyclosetosubjec;veanalysiswasrevealed.
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Figure8:StarwarsEpisodeII–with85dBthresholdandshowingsinglemetric
Figure9:MasterandCommander
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Figure10:MissionImpossible3
Figure11:VeerZara
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Butacoupleoffilmsseemtocomeoutwithtoolowanumberwhencomparedwiththe
subjec;velevel.No;ceablewasSlumdogMillionaire,wherealotofenergywasconcentratedin
theregionbetween80dBLeq(m)and85dBLeq(m).
ThresholdSelecIon:
Wetooksomeselected;tles,andcomparedan85dBthresholdwitha70dBthreshold,
andtheresultsareshowninFigure12.
Figure12:Comparisonof85dBand70dBthresholds
Next,wemadeananalysisof“loud”moviesversus“quiet”moviesatdifferentthresholds,as
showninFigure13.
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Figure13:Comparisonof“loud”and“quiet”moviesatdifferentthresholds
Thefinalconclusionwasthatan80dBthresholdgavethebesthierarchy,andacomparisonof
85dBand80dBcanbeseeninFigure14.Notonlyagoodhierarchy,butmoreevenlyspread.
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Figure14:Effectofchangingthresholdfrom85dBto80dB–normalizedto
VeerZara,theloudestmoviemeasuredtodate
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WindowduraIon:
Asstatedearlier,tooshortawindowandpeaklevelswouldberestricted.Toolongawindow
couldallowabuse.10minutesseemsaboutright.Thiswasasubjec;vecall,butminor
revisionswouldprobablynotcausemajorchangesinthehierarchy.
SourceContent:
AllthematerialcitedinthispapercamefromDCPpackages,withtheexcep;onofFigure19
whichforhistoricalreferenceshowstheLeq(m10)ofthe35mmDolbyDigitalversionof
ApocalypseNow.
WehavecarriedonmeasuringselectedfeaturesandafewoftheseareshowninFigures15,16,
17,18.
Figure15:U23D--80dBthreshold
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Figure16:Birdman
Figure17:Hobbit3
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Figure18:AmericanSniper
Figure19:ApocalypseNow–35mmDolbyDigital
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SomeselectedfilmsareshowninorderofLeq(m10)inthetable:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
U23D
MadMax:FuryRoad
TransformersIII MissionImpossibleIII
StarWars:TheForceAwakens
ApocalypseNow Tron:Legacy
SlumdogMillionaire
Hobbit3 Skyfall
AmericanSniper MoonriseKingdom
Birdman GrandTorino
528
422
360
356
317
255
240
231
225
170
139
86
77
0
Conclusion:
Onceagain,weareinnowaysugges;ngthatfeaturefilmsshouldberegulated.Theprocedure
describedisprimarilybeingofferedasamuchbeeermethodofderivinganumberwhich
reportsthesubjec;veloudnessofamovie–farbeeerthanmeasuringthepeaklevelsreached.
Anditshouldbepointedoutthatthemetricdescribedhasnoabsolutevalue–itsvalueis
purelyrela;ve,revealingwhichfilmsaresubjec;velylouderthanothers.
Reference:
1. “Aremoviestooloud?”SMPTEJournal,vol.107,pg30,1998
2. ISO21727,“MethodofMeasurementofPerceivedLoudnessofShortDura;onMo;onpictureAudioMaterial.”
Notes:
1. Someofthematerialcontainedinthispaperisupdatedcontentfrompresenta;ons
madetotheSMPTEOctober2007andTheHollywoodPostAlliance,February2009.
2. ThispaperiscopyrightbytheSMPTE,andhasbeenapprovedforpublica;oninthe
SMPTEMo;onImagingJournal.
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