Auditory Sensation

Announcements
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Auditory Sensation
Remember: Perception Journals are due on Thursday 11/19
No class Tuesday before Thanksgiving (11/24)
Perception journal examples posted on Blackboard
Exam 3: Thursday 11/12
•  Basics of hearing
•  Perception of loudness
•  Perception of pitch
•  Perception of timbre
Shepard tone
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http://www.tutis.ca/Senses/L9Auditory/L9Auditory.swf
What is hearing good for?
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What is hearing good for?
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Blindness cuts me off from
things; deafness cuts me off
from people. Helen Keller
Detecting presence of something or someone, even things out of sight
Localization of sound sources ( where )
Recognition of sound sources ( what )
Communication
–  Content (the message)
–  Source (the messenger)
–  Affect (the mood)
•  Navigation/motor coordination
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Walking
Typing
Talking
Echolocation
•  Enjoyment of music (music can calm, can inspire and energize)
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Hearing
Name that Sound!
!  We hear by detecting mechanical vibrations traveling through air (or some other
medium such as water)
!  Speed of sound in air: 770 mi/hour
!  Water = ~4,000 mi/hour, Metal = ~12,000 mi/hour, Diamond = ~27,000 mi/hour
Humans and other animals are able to identify
a wide variety of sounds, presumably based
on their timbres and rhythms.
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Hearing
Hearing
We hear by detecting mechanical vibrations traveling
through air (or some other medium such as water)
We hear by detecting mechanical vibrations traveling
through air (or some other medium such as water)
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Hearing
Pure Tones
Two spaceships were traveling trough outer space. One of
them suddenly exploded. The accident did not impact the
other spaceship, but the explosion was exceedingly loud causing hearing problems in many of the crew members.
What is the problem with this story?
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Hearing
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Pure Tones in Natural Environment
!  Sound waves are characterized by their frequency and intensity
!  sound pitch is our subjective experience associated sound frequency.
!  loudness is our subjective experience associated sound intensity
Frequency
Different sound frequency
Pure tones (only ONE freq)
Different sound intensity
high frequency = short period
low frequency = long period
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Complex, natural sounds
Speech sounds
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Auditory Sensation
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Loudness and Intensity
loudness = our subjective experience of sound intensity.
Rule 1: All else being equal, the higher the intensity, the greater the loudness.
•  Basics of hearing
•  Perception of loudness
•  Perception of pitch
•  Perception of timbre
Higher intensity, higher
loudness
http://www.tutis.ca/Senses/L9Auditory/L9Auditory.swf
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Lower intensity, lower loudness
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Rule 2: The relationship between intensity and loudness is
nonlinear. Doubling intensity does not double loudness.
In order to double loudness, intensity must be increased by a
factor of 3.16, or by 10 dB This is called the 10 dB rule.
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Rule 2: The relationship between intensity and loudness is
nonlinear. Doubling intensity does not double loudness.
In order to double loudness, intensity must be increased by a
factor of 3.16, or by 10 dB This is called the 10 dB rule.
Two signals differing by 10 dB:
Rule 3: Loudness is strongly affected by the frequency of the
signal. If intensity is held constant, a mid-frequency signal (in
the range from ~1000-4000 Hz) will be louder than lower or
higher frequency signals.
(500 Hz sinusoids)
125 Hz, 3000 Hz, 8000 Hz
The 3000 Hz signal should appear louder than the 125 or the
8000 signal, despite the fact that their intensities are equal.
The 10 dB rule means that a 70 dB signal is twice as loud as a 60 dB
signal, four times as loud as a 50 dB signal, eight times as loud as a 40
dB signal, etc.
• dB = 20 log (p1/p0)
• [20 x log10 (3.16) = 20 x .5 = 10 dB].
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The Audibility Curve
Range of human hearing: 20Hz to 20,000 Hz
A psychophysical function from a set of psychometric functions
One can determine what frequencies an individual is most
sensitive to by measuring an audibility curve…
0.25
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Stimulus intensity
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audible sound frequencies
Percent "detected"
0.50
Percentage "detected"
Percent "detect"
0.75
0.00
0
1.00
0.75
0.50
0.25
0.00
0
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8 10 12
1.00
0.75
0.50
0.25
0.00
0
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Stimulus intensity
Stimulus intensity
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Intensity threshold
Threshold intensity (dB)
1.00
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inaudible sound frequencies
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100
1000
10000
Frequency (Hz)
Sound frequency (Hz)
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Sound frequency
Auditory Sensation
!  sound pitch is our subjective experience of sound frequency.
!  The ranges of sound frequencies we are able to hear depends on a number of
factors: e.g., species, age, previous exposure to sounds & individual variability
•  Basics of hearing
Sound frequency (Hz)
•  Perception of loudness
•  Perception of pitch
•  Perception of timbre
!  This example sound is a pure tone containing only one sound frequency
http://www.tutis.ca/Senses/L9Auditory/L9Auditory.swf
!  Natural sounds typically contain
multiple sound frequencies
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300 vs. 350 Hz are easier to distinguish than 3000 vs.
3050 Hz
That is, the difference in perceived pitch between 300 and
350 Hz is NOT the same as the difference in pitch between
3000 and 3050 Hz, even though the physical differences in
frequencies are the same.
300-350
The Weber Fraction
(the JND divided by the magnitude of the standard)
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Just noticeable difference
(diameter)
Rule 1: The ear is more sensitive to frequency differences
in the low frequencies than the higher frequencies. This
means that:
JND
Standard circle size
(diameter)
Weber s law: Increases in intensity that are
just noticeably different to an observer are
constant fraction of stimulus intensity
3000-3050
JND
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Weber s law: Weber fraction is constant
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Pitch and Fundamental Frequency: F0
Rule 2: All else being equal, the higher the F0, the higher the perceived pitch.
Frequency Discrimination
200 Hz
800 Hz
2200 Hz
202 Hz
810 Hz
2220 Hz
205 Hz
820 Hz
2250 Hz
F0 = the lowest frequency in a harmonic series.
Lower F0, lower pitch
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Pitch and Fundamental Frequency: F0
Higher F0, higher pitch
high frequency = short period
low frequency = long period
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The problem of missing fundamental
Rule 2: All else being equal, the higher the F0, the higher the perceived pitch.
F0 = the lowest frequency in a harmonic series.
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http://auditoryneuroscience.com/topics/periodic-sounds-must-have-harmonic-structure
http://auditoryneuroscience.com/topics/missing-fundamental
The Problem of the Missing Fundamental
Conclusion: The fundamental does not need to be
physically present in the signal for a listener to hear a
pitch corresponding to where f0 ought to be.
What Explains This?
Even with f0 removed, a signal remains periodic at the
original f0.
Normal F0:
F0 Removed:
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What does all this mean?
Rule 3: The sensation of pitch is probably based
on a measurement of the fundamental period. It
is definitely not based on a measurement of the
lowest frequency harmonic in a harmonic
spectrum.
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Fingernails on chalkboard
(why is it so annoying?)
!  Even Aristotle pondered about it (~ 335 BC)
!  Halpern, Blake & Hillenbrands (1986) looked at its different frequency
components, and found that….
Possible explanation? (via Google :-)
!  the slip and stick motion is similar to the feeling of teeth scraping together, or
teeth being scraped by something too hard to chew. Perhaps the reaction comes
from the need to preserve one‘s teeth for eating meat.
Fingers scraping the chalkboard activate amygdala
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Let s filter this sound
Low pass filter
High pass filter
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This sound is similar to some warning calls emitted by monkeys.
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This sound is similar to some warning calls emitted by monkeys.
Auditory Sensation
•  Basics of hearing
•  Perception of loudness
•  Perception of pitch
•  Perception of timbre
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http://www.tutis.ca/Senses/L9Auditory/L9Auditory.swf
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Musical Timbre
Timbre: (also known as sound quality)
When two sounds are heard that match for pitch, loudness, and
duration, and a difference can still be heard between the two sounds,
that difference is called timbre.
For example: a clarinet, a saxophone, and a piano all play a middle C at
the same loudness and same duration. Each of these instruments has a
unique sound quality. This difference is called timbre or sound quality.
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Frequency
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Timbre and Spectrum Envelope
Timbre: (also known as sound quality)
When two sounds are heard that match for pitch, loudness, and
duration, and a difference can still be heard between the two sounds,
that difference is called timbre.
For example: a clarinet, a saxophone, and a piano all play a middle C at
the same loudness and same duration. Each of these instruments has a
unique sound quality. This difference is called timbre or sound quality.
Timbre differences between one musical
instrument and another are related to
differences in spectrum envelope -differences in the relative amplitudes of the
individual frequencies.
There are two physical correlates of timbre:
spectrum envelope
amplitude envelope
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Synthesized Sounds Differing in Spectrum Envelope
Synthesized Sounds Differing in Spectrum Envelope
Flute
Note the similarities in pitch (due to constant F0/harmonic
spacing) and the differences in timbre or sound quality.
Clarinet
Horn
Note the similarities in pitch (due to constant F0/harmonic
spacing) and the differences in timbre or sound quality.
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http://auditoryneuroscience.com/topics/same-melody-different-timbre
Amplitude Envelope
Same melody, same spectrum envelope, different amplitude envelopes (i.e., different
attack and decay characteristics).
Note differences in timbre or sound quality as the amplitude envelope varies.
Timber is also affected by amplitude envelope. Amplitude envelope is a
smooth line drawn to enclose a sound wave. It is also sometimes called the
amplitude contour or energy contour of the sound wave. Amplitude envelope
refers to the characteristics of the way sounds are turned on and turned off.
The four signals below are sinusoids that differ in their amplitude envelopes:
(1)
(2)
(3)
(4)
(5)
(6)
Leading edge = attack; Trailing edge = decay
The attack especially has a large effect on timbre.
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Leading edge = attack; Trailing edge = decay
The attack especially has a large effect on timbre
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Auditory Sensation
There are many examples in music of timbre differences related to
differences in amplitude envelope:
Plucked vs. bowed stringed instruments
•  Basics of hearing
The damping pedal on a piano
The difference in sound quality between a hammered string (e.g.,
a piano) and a string that is plucked by a quill (e.g., a
harpsichord).
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•  Perception of loudness
•  Perception of pitch
•  Perception of timbre
http://www.tutis.ca/Senses/L9Auditory/L9Auditory.swf
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Sometimes they behave so strangely
http://www.radiolab.org/2007/sep/24/
How to break a glass with sound
Diana Deutsch
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http://www.youtube.com/watch?v=9KuwJXMQUdc&feature=related