Chapter 6: (The Human Ear)

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Chapter 6(The Human Ear)
1. Peripheral Auditory System2. Place Theory of
Hearing3. Amplitude Response of the Ear4.
Logarithms and Sound Intensity Scales 5.
Periodicity Pitch and Fundamental Tracking 6.
Aural Harmonics and Combination Tones 7. Ohms
Law of Hearing 8. Masking 9. Binaural Effects 10.
Hearing Loss
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(The Human Voice)
11. Anatomy of the Vocal Tract 12. Vocal
Formants 13. Analysis of Vocal Sounds
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Dynamic Range of ear

• Frequency range 20 Hz 20 kHz
• (factor of 1000)
• Range of eye 0.400- 0.700 microns
• (factor of 2)
• Intensity range 1 to 1012
• Range of eye 1-1,000,000 (106)

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Peripheral Auditory System
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Cross section of the Cochlea
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Guinea Pig Hair Cells
Similar in humans, chinchillas, cats and guinea
pigs
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The Place Theory of Hearing
From Juan G. Roederer, The Physics and
Psychophysics of Music
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Features of the Place Theory

• Correlation of frequency with position of
  maximum response (higher frequencies closer to
  oval window at base of cochlea)
• 20-5000 Hz frequency range gt2/3 of membrane
  length
• Remaining frequencies (5,000-20,000 Hz
• squeezed into remaining lt1/3
• 4. Equal frequency ratios occupy the same
  distance along membrane

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Experimental basisfor the Place theory

• 1. The Critical Band
• 2. The Frequency JND
• 3. The Limit of Frequency Discrimination
• and its analog experiment
• 4. Sharpening

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The Critical Band
15 in frequency, greater at lower frequencies
From Juan G. Roederer, The Physics and
Psychophysics of Music
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The Just Noticeable Difference
0.6 in frequency, greater at lower frequencies
From Juan G. Roederer, The Physics and
Psychophysics of Music
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Limit of frequency discrimination(two tones)
7 for low frequencies, 15 for higher
frequencies
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Analog experimentusing the armas basilar
membrane
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Effect ofSharpening
The JND is less for complex waves
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Experiment Summary
From Juan G. Roederer, The Physics and
Psychophysics of Music
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Escher Waterfall
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Escher Staircase
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Shepards Tones
Roger N. Shepard Circularity in Judgements of
Relative Pitch Journal of the Acoustical
Society of America, 1964
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A Pair ofParadoxes
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Shepards tones in music

• Voice of the Computer
• Jean-Claude Risset
• Computer Suite from Little Boy
• Flight and Count-down
• Fall (uses downward glissando Shepards tones to
  represent the fall of the atomic bomb on
  Hiroshima
• Contra-Apotheosis

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Fletcher-Munson (Equal Loudness) Curves
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Sound Intensity Level Scale(SIL)Units of bels
or decibels

• Physics scale
• Equal intensity ratios mean
• equal steps of loudness
• 3. Intensity JND

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Loudness Level scalePhons

• Subjective scale
• Accounts for variation
• of loudness with frequency
• 3. More useful in describing
• hearing

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The decibel scale
SIL SIL0 10 log (I/Io)
log 1 0.0 log 2 0.3 log 3 0.5 log 4
0.6 log 5 0.7
log 6 0.8 log 7 0.85 log 8 0.9 log 9
0.95 log 10 1.0
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Examples using decibels

• Adding two equal signals
• Multiplying a signal by 3
• Multiplying a signal by 10
• Multiplying a signal by 1.25
• Demonstration H5-21 Three Decibels
• Question of the Week 149
• Question of the Week 150
• Consultation as expert acoustic witness

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Periodicity PitchandFundamental Tracking
Psychological phenomenon
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Aural HarmonicsandCombination Tones
Created by non-linearities primarily in the bone
chain of the middle ear
Physical phenomenon
Sum Tone f nf1 mf2
Difference Tone f- nf1 - mf2
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Aural Harmonics
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Combination Tone Experiment
n m sum f difference f- 1 1 1200 Hz 200
Hz 1 2 1900 Hz 900 Hz 2 1 1700 Hz 300
Hz 2 2 2400 Hz 400 Hz
f1 500 Hz f2 700 Hz
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Ohms Law of Hearing(excellent
approximation)Second order (quality)
beats(counterexample to Ohms Law)Masking(compl
ication of Critical Band)
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Quality Beats (Second-order beats)
Fundamental with mis-tuned 2nd harmonic
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Source of Masking
From Thomas Rossing, The Science of Sound
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Masking Curves

• Threshold of hearing for pure tone
• Masking by 365 Hz to 455 Hz 80 dB noise band
• Masking by 400 Hz 80 dB tone

From Donald Hall Musical Acoustics, Second
Edition
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Steady-state tone quality

• Number and amplitude of overtones
• Inharmonicities
• Periodicity pitch and
• fundamental tracking
• 4. Difference tones (enhance fundamental)
• 5. Critical Band and Masking (formants)

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Musical Effects of theCritical Band and Masking

• Open chords sound more clear than closed chords,
  especially using bass notes
• Close notes sound sound homophonic chords
  predominate
• Spread out notes sound polyphonic individual
  lines are more easily identified
• Eg Use of low chord in piano music affected by
  historical development of the piano

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Binaural Effects

• Binaural beats and diplacusis
• Localization of sounds
• (low f 500-800Hz, high f gt 1000Hz)
• 3. Click illusions
• (monaural and binaural)
• 4. Precedence effect

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Hearing Loss

• Temporary threshold shifts
• Exposure to noise
• Reaction to drugs
• 2. Permanent hearing loss
• Noise or drug exposure
• Natural aging (presbycusis)
• Rubella during pregnancy
• 3. Tinnitus or ringing in ear
• (permanent or temporary)
• Noise or drugs

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Treatment of Hearing Loss

• Diagnosis using audiogram
• Surgery for outer and middle ear
• No correction for central
• auditory system problems
• 4. Hearing aid corrects threshold
• problems
• 5. Cochlear Implants

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Cochlear Implant - Overview
Source Prof. Graeme Clark, The Bionic Ear
Institute
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Cochlear Implant - Detail
Source Prof. Leslie M. Collins, Duke University
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Cochlear Implant References
Cochlear Implant Association, Inc. http//www.cici
.org/
The Bionic Ear Institute The University of
Melbourne http//www.bionicear.org/bei/index2.html
Advanced Bionics http//www.advancedbionics.com/
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TheHumanVocalTract
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Closed tube system(formation of vowel sounds)
Shorter length Raises frequency
Moving center node toward closed end raises
frequency by shortening wavelength
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Vocal Formant spectra
OO
AH
EE
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Vocal Spectrogram of Formants
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Formants for vowel sounds
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Constancy of formant frequencyasSinging
frequency changes
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TheSingersFormant
Averaged spectral energy distribution Light
ordinary speech Dark orchestral
accompaniment Brown Good singer with
orchestra Johan Sundberg The Acoustics of the
Singing Voice Sci. Amer., March 1977
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Formation of Sibilants
Unvoiced sss
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Formation of Sibilants
Voiced zzz
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Audio Spectrograms
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Voice and Synthesizer wow
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Computerized Speech Laboratory
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Matching vocal spectrograms
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1. Helium Voiceand Sulfur Hexafluoride Voice
2. Tibetan Monks and the Tantric Rituals
3. The Harmonic Choir
4. Kronos String Quartet with Tuvan Throat Singers
5. Falsetto singing and countertenor singers
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Spectrograms of Bird Calls
What birds are they?
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The End