INSTRUCTIONAL OBJECTIVES:

1
INSTRUCTIONAL OBJECTIVES

• Indicate frequency, amplitude and phase on a
  diagram of a simple sine wave. List the units of
  measurement corresponding to each feature and the
  normal human range.
• Define Fourier analysis and describe amplitude
  and phase spectra. Explain why 2 different
  musical instruments sound different even when
  playing the same note.
• 3. Identify the structures in the outer, middle
  and inner ears.
• 4. Describe 2 ways in which the middle ear
  functions to amplify the sound pressure reaching
  the inner ear.
• 5. Define the acoustic reflex and name the 2
  muscles involved.

2
Physical stimulus for hearing
sound is produced by the physical vibration of
objects
Coren et al. (2004)
compression air molecules bunch together
rarefaction air molecules spread apart
3
Physical stimulus for hearing
sound pressure wave
1 cycle
Coren et al. (2004)
phase part of cycle the sound pressure wave has
reached at a given point in time measured in
degrees
amplitude (intensity) magnitude of displacement
of sound pressure wave
frequency rate of fluctuation of sound
pressure measured in cycles/second or Hertz (Hz)
4
Physical stimulus for hearing
phase is often used to compare the timing of 2
sound waves
Mather (2006)
waves (b), (c) and (d )are phase-shifted by the
amount shown in degrees relative to wave (a)
5
sound pressure
Physical stimulus for hearing

• force against eardrum--dynes/cm2
• 0.0002 dynes/cm 2 - absolute threshold (1000 Hz)
• 2000 dynes /cm 2 - painful
• convert to log scale called sound pressure
  level--decibels (dB)
• dB conversion -- db 20 log (P/Po)
• (P is sound pressure of tone Po is reference
  pressure of 0.0002 dynes/cm2)

6
Physical stimulus for hearing
decibel values for common sounds
just detectable 1000 Hz tone
Fig 9.4
7
Physical stimulus for hearing
range of human hearing
Fig 9.3
8
Physical stimulus for hearing
frequency range of hearing for different species
Blake Sekuler (2006)
humans 20-20,000 Hz
9
Physical stimulus for hearing
tuning forks produce pure tones, represented by
single sine waves
frequency corresponds to perceived pitch
sound pressure level (intensity) corresponds to
perceived loudness
10
Physical stimulus for hearing
most sounds are not pure tones
periodic
non-periodic
Schmidt (1986)
11
Physical stimulus for hearing
all sounds can be described as a set of sine
waves (Fourier analysis)
Coren et al. (2004)
12
Physical stimulus for hearing
fundamental lowest sinewave frequency in a
complex sound
harmonics higher frequency components integer
multiples of fundamental
13
Physical stimulus for hearing
Fourier analysis of clarinet note
amplitude change over time produced by continuous
clarinet note
sinewave components of the clarinet note (vary in
frequency, amplitude, phase)
amplitude spectrum
phase spectrum
Fourier spectra for clarinet note
www.sinauer.com/wolfe2e/chap9/fourierF.htm
Mather (2006)
14
Physical stimulus for hearing
timbre
Coren et al. (2004)
relative level of harmonics determines
psychological attribute of quality or timbre (why
musical instruments sound different)
15
Physical stimulus for hearing
sinewave components of 2 instruments playing a
fundamental frequency of 196 Hz
differences in harmonics (overtones) determine
timbre
16
Physical stimulus for hearing
Coren et al. (2004)
different timbre due to more low frequencies in
position B
same pitch because fundamental frequency is the
same
17
Anatomy of the peripheral auditory system
outer ear gathers sound energy funnels it to
the tympanic membrane (eardrum)
18
Anatomy of the peripheral auditory system
shape of pinna helps with sound localization
Fig 9.9
length shape of ear canal enhances sounds
between 2000 6000 Hz
19
Anatomy of the peripheral auditory system
middle ear amplifies sound energy
impedance matching amplification of sound
energy to reduce loss by reflection at oval
window (air/fluid boundary)
20
impedance matching
Anatomy of the peripheral auditory system

• tympanic membrane larger than stapes footplate
  (55 mm23.2 mm2)
• increases pressure change at oval window
  (pressureforce/unit area like high heels)
• ossicles act like levers
• increases force at stapes by a factor of 1.3
  (like a teeter totter)

21
Anatomy of the peripheral auditory system
middle ear protects inner ear from potentially
harmful loud sounds
acoustic reflex in response to prolonged loud
sounds, tensor tympani stapedius muscles
contract to reduce magnitude of auditory signal
transmitted to ear
22
Anatomy of the peripheral auditory system
eustachian tube equalizes air pressure between
middle and outer ear
23
Final exam Wednesday, December 16, 330-530 pm
Midterm exam details
Tuesday, Oct 27 lectures Sept 10 Oct 22
textbook chapters 1-3 (all pages) 9 (pgs
219-237) Cornsweet article on staircase method
web essay 3.3 (www.sinauer.com/wolfe2e/chap3/image
soncortexF.htm)
45 multiple choice questions (1 mark each) 3
short answer questions (5 marks each)
bring pencil for scantron pen for short answers
student ID