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(The Human Ear)1. Peripheral Auditory System2. Place Theory of Hearing3. Amplitude Response of the Ear4. Logarithms and Sound Intensity Scales5. Periodicity Pitch and Fundamental Tracking6. Aural Harmonics and Combination Tones7. Ohm’s Law of Hearing8. Masking9. Binaural Effects10. Hearing Loss
(The Human Voice)
11. Anatomy of the Vocal Tract12. Vocal Formants13. Analysis of Vocal Sounds
“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)
Peripheral Auditory System
Cross section of the Cochlea
Guinea Pig “Hair Cells”
Similar in humans, chinchillas, cats and guinea pigs
The “Place Theory” of Hearing
From: Juan G. Roederer, The Physics and Psychophysics of Music
Features of the “Place Theory”1. Correlation of frequency with position of
maximum response (higher frequencies closer to oval window at base of cochlea)
2. 20-5000 Hz frequency range >2/3 of membrane length
3. Remaining frequencies (5,000-20,000 Hz
squeezed into remaining <1/3
4. Equal frequency ratios occupy the same distance along membrane
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
The Critical Band
~15% in frequency, greater at lower frequencies
From: Juan G. Roederer, The Physics and Psychophysics of Music
The Just Noticeable Difference
~0.6% in frequency, greater at lower frequencies
From: Juan G. Roederer, The Physics and Psychophysics of Music
Limit of frequency discrimination
(two tones)
~7% for low frequencies, ~15% for higher frequencies
Analog experimentusing the arm
as basilar membrane
Effect of“Sharpening”
The JND is less for complex waves
Experiment Summary
From: Juan G. Roederer, The Physics and Psychophysics of Music
Escher: Waterfall
Escher: Staircase
Shepard’s Tones
Roger N. Shepard: Circularity in Judgements of Relative Pitch; Journal of the Acoustical Society of America, 1964
A Pair ofParadoxes
Shepard’s tones in musicVoice of the ComputerJean-Claude Risset:
Computer Suite from “Little Boy”
I. Flight and Count-down
II. Fall (uses downward glissando Shepard’s tones to represent the fall of the atomic bomb on Hiroshima
III. Contra-Apotheosis
Fletcher-Munson (Equal Loudness) Curves
Sound Intensity Level Scale(SIL)
Units of bels or decibels
1. “Physics” scale2. Equal intensity ratios mean
equal steps of loudness3. Intensity JND
Loudness Level scale“Phons”
1. “Subjective” scale2. Accounts for variation
of loudness with frequency3. More useful in describing
hearing
The decibel scale
SIL = SIL0 + 10 log (I/Io)
log 1 = 0.0log 2 = 0.3log 3 = 0.5log 4 = 0.6log 5 = 0.7
log 6 = 0.8log 7 = 0.85log 8 = 0.9log 9 = 0.95log 10 = 1.0
Examples using decibels1. Adding two equal signals2. Multiplying a signal by 33. Multiplying a signal by 104. Multiplying a signal by 1.255. Demonstration H5-21 Three Decibels6. Question of the Week #1497. Question of the Week #1508. Consultation as expert acoustic witness
Periodicity Pitchand
Fundamental TrackingPsychological phenomenon
Aural Harmonicsand
Combination Tones
Sum Tone: f+ = nf1 + mf2
Difference Tone: f- = | nf1 - mf2 |
Created by non-linearities primarilyin the bone chain of the middle ear
Physical phenomenon
Aural Harmonics
Combination Tone Experimentn m sum: f+ difference: f-
1 1 1200 Hz 200 Hz
1 2 1900 Hz 900 Hz2 1 1700 Hz 300 Hz2 2 2400 Hz 400 Hz
f1 = 500 Hz f2 = 700 Hz
Ohm’s Law of Hearing(excellent approximation)
Second order (quality) beats(counterexample to Ohm’s Law)
Masking(complication of Critical Band)
Quality Beats (Second-order beats)
Fundamental with mis-tuned 2nd harmonic
Source of Masking
From: Thomas Rossing, The Science of Sound
Masking Curves
From: Donald Hall: Musical Acoustics, Second Edition
a. Threshold of hearing for pure toneb. Masking by 365 Hz to 455 Hz 80 dB noise bandc. Masking by 400 Hz 80 dB tone
Steady-state tone quality
1. Number and amplitude of overtones2. Inharmonicities3. Periodicity pitch and
fundamental tracking 4. Difference tones (enhance fundamental)5. Critical Band and Masking (formants)
Musical Effects of theCritical Band and Masking
1. Open chords sound more clear than closed chords, especially using bass notes
2. Close notes sound sound homophonic – chords predominate
3. Spread out notes sound polyphonic – individual lines are more easily identified
4. Eg: Use of low chord in piano music affected by historical development of the piano
Binaural Effects
1. Binaural beats and diplacusis 2. Localization of sounds
(low f = 500-800Hz, high f > 1000Hz)3. Click illusions
(monaural and binaural)4. Precedence effect
Hearing Loss1. Temporary threshold shifts
Exposure to noiseReaction to drugs
2. Permanent hearing lossNoise or drug exposureNatural aging (presbycusis)Rubella during pregnancy
3. Tinnitus or ringing in ear (permanent or temporary)Noise or drugs
Treatment of Hearing Loss
1. Diagnosis using audiogram2. Surgery for outer and middle ear3. No correction for central
auditory system problems4. Hearing aid corrects threshold
problems5. Cochlear Implants
Cochlear Implant - Overview
Source: Prof. Graeme Clark, The Bionic Ear Institute
Cochlear Implant - Detail
Source: Prof. Leslie M. Collins, Duke University
Cochlear Implant ReferencesCochlear Implant Association, Inc.
http://www.cici.org/
The Bionic Ear InstituteThe University of Melbourne
http://www.bionicear.org/bei/index2.html
Advanced Bionicshttp://www.advancedbionics.com/
TheHumanVocalTract
Closed tube system(formation of vowel sounds)
Shorter lengthRaises frequency
Moving center nodetoward closed endraises frequency byshortening wavelength
Vocal Formant spectra
“OO”
“AH”
“EE”
Vocal Spectrogram of Formants
Formants for vowel sounds
Constancy of formant frequencyas
Singing frequency changes
TheSingersFormant
Averaged spectral energy distribution:Light: ordinary speechDark: orchestral accompanimentBrown: Good singer with orchestra
Johan Sundberg: The Acoustics of the Singing Voice; Sci. Amer., March 1977
Formation of Sibilants
Unvoiced:“sss”
Formation of Sibilants
Voiced:“zzz”
Audio Spectrograms
Voice and Synthesizer “wow”
Computerized Speech Laboratory
Matching vocal spectrograms
1. Helium Voiceand Sulfur Hexafluoride Voice
2. Tibetan Monks and the
Tantric Rituals
3. The Harmonic Choir
4. Kronos String Quartetwith Tuvan Throat Singers
5. Falsetto singing andcountertenor singers
Spectrograms of Bird Calls
What birds are they?
The End