(The Human Ear) 1. Peripheral Auditory System 2. Place Theory of Hearing 3. Amplitude Response of the Ear 4. Logarithms and Sound Intensity Scales 5. Periodicity Pitch and Fundamental Tracking 6. Aural Harmonics and Combination Tones 7. Ohm’s Law of Hearing 8. Masking 9. Binaural Effects 10. Hearing Loss

(The Human Voice) 11. Anatomy of the Vocal Tract 12. Vocal Formants 13. Analysis of Vocal Sounds

“Dynamic Range” of ear Frequency range: 20 Hz – 20 kHz (factor of 1000) Range of eye ~ microns (factor of 2) Intensity range: 1 to Range of eye ~ 1-1,000,000 (10 6 )

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) 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 basis for 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 experiment using 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 of Paradoxes

Shepard’s tones in music Voice of the Computer Jean-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” scale 2.Equal intensity ratios mean equal steps of loudness 3. Intensity JND

Loudness Level scale “Phons” 1.“Subjective” scale 2.Accounts for variation of loudness with frequency 3. More useful in describing hearing

The decibel scale SIL = SIL log (I/I o ) 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

Examples using decibels 1.Adding two equal signals 2.Multiplying a signal by 3 3.Multiplying a signal by 10 4.Multiplying a signal by Demonstration H5-21 Three DecibelsDemonstration H5-21 Three Decibels 6.Question of the Week #149Question of the Week #149 7.Question of the Week #150Question of the Week #150 8.Consultation as expert acoustic witness

Periodicity Pitch and Fundamental Tracking Psychological phenomenon

Aural Harmonics and Combination Tones Sum Tone: f + = nf 1 + mf 2 Difference Tone: f - = | nf 1 - mf 2 | Created by non-linearities primarily in the bone chain of the middle ear Physical phenomenon

Aural Harmonics

Combination Tone Experiment nmsum: f + difference: f Hz200 Hz Hz900 Hz Hz300 Hz Hz400 Hz f 1 = 500 Hzf 2 = 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 2 nd 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 tone b.Masking by 365 Hz to 455 Hz 80 dB noise band c.Masking by 400 Hz 80 dB tone

Steady-state tone quality 1.Number and amplitude of overtones 2.Inharmonicities 3.Periodicity pitch and fundamental tracking 4. Difference tones (enhance fundamental) 5. Critical Band and Masking (formants)

Musical Effects of the Critical 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 = Hz, high f > 1000Hz) 3. Click illusions (monaural and binaural) 4. Precedence effect

Hearing Loss 1.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

Treatment of Hearing Loss 1.Diagnosis using audiogram 2.Surgery for outer and middle ear 3.No correction for central auditory system problems 4. Hearing aid corrects threshold problems 5. 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 References Cochlear Implant Association, Inc. The Bionic Ear Institute The University of Melbourne Advanced Bionics

The Human Vocal Tract

Closed tube system (formation of vowel sounds) Shorter length Raises frequency Moving center node toward closed end raises frequency by shortening wavelength

Vocal Formant spectra “OO” “AH” “EE”

Vocal Spectrogram of Formants

Formants for vowel sounds

Constancy of formant frequency as Singing frequency changes

The Singers Formant 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

Formation of Sibilants Unvoiced: “sss”

Formation of Sibilants Voiced: “zzz”

Audio Spectrograms

Voice and Synthesizer “wow”

Computerized Speech Laboratory

Matching vocal spectrograms

1. Helium Voice and 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

Spectrograms of Bird Calls What birds are they?

The End