(the human ear) 1. peripheral auditory system 2. place theory of hearing 3. amplitude response of...

(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