PSY280H1 Lecture Notes - Musical Tone, Fundamental Frequency, Middle Ear

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Published on 20 Apr 2013
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CH11 Sound, the Auditory System and Pitch Perception
The Sound Stimulus
SOUND two definitions, physical & perceptual
o PHYSICAL: sound is pressure changes in the air or other medium
o PERCEPTUAL: sound is the experience we have when we hear
Sound as Pressure Changes
o Sound stimulus occurs when an object’s movements/vibrations cause
pressure changes in air, water, any elastic medium surrounding the
object ex. loudspeaker vibrations affect surrounding air by:
CONDENSATION diaphragm moves out push air molecules
together, increase nearby molecule density
RAREFACTION speaker diaphragm moves back in pull air
molecules in to fill gap, decrease air pressure
Repetition thousands time per second pattern of alternating
high-low pressure regions in air spreads out SOUND WAVE
B/c neighboring air molecules affect each other
Air pressure changes moving outwards from sound source
Air molecules in medium moves back/forth
Osculates around point but stays around same place
Pressure changes: Pure Tones
o PURE TONES occurs when pressure changes in air occur in a
pattern described by a SINE WAVE mathematical function
Ex. tuning forks, high pitched notes
Can be described by particular amplitude and frequency
o AMPLITUDE the size of the pressure change
Physical property of amplitude associated w/ experience of
loudness; higher amplitude = louder sounds
Measured in DECIBELS (dB) logarithmic scale of measurement
dB SPL = 20 * log(p/p0)
where, p = sound pressure of the stimulus
and, p0 = 20 micropascals, standard sound pressure,
pressure near the threshold for human hearing
SPL (SOUND PRESSURE LEVEL) indicates we used the
standard pressure of 20 micropascals as p0
o FREQUENCY number of times per sec. the pressure change repeats
Physical property of frequency associated w/ experience of
pitch; higher frequency = higher pitch
Measured in Hertz (Hz) Hz is number of cycle per second
Humans can perceive in 20 20 000 Hz range
o Pure tones rare in environments but simple to study
Usually sound in environment have more complex waveforms
Pressure changes: complex tones
o COMPLEX TONES waveform != a SINE WAVE, but a combination
is a PERIODIC TONE the waveform repeats
Repetition rate of complex tone is called the
FUNDAMENTAL FREQUENCY of the tone
focus on sound from musical instruments
Periodic complex tones consist of number of pure tones
o Can build a complex tone by ADDITIVE SYNTHESIS = number of sine-
wave components are added together to create a complex tone
FUNDAMENTAL FREQUENCY starting point for creating a
complex tone, the first pure tone
All additional tones (HARMONICS) must be a multiple of
the fundamental frequency
o FREQUENCY SPECTRA another way to represent the harmonic
components of a complex tone
Horizontal position = frequency; Vertical position = amplitude
Perceiving sound
LOUDNESS most closely associated w/ amplitude or sound pressure,
level of auditory stimulus; associated w/ dB
o Increase sound by 10dB = roughly double loudness
Decibels = physical measure air pressure
Loudness = physiological a perception
PITCH the attribute of auditory sensation in terms of which sounds may
be ordered on a musical scale perceptual quality of “high” or “low”
o Closely related to physical property of frequency
Low fundamental frequencies associated w/ low pitch
High fundamental frequencies associated w/ high pitch
o TONE HEIGHT perceptual experience of increasing pitch that
accompanies increases in a tone’s fundamental frequency
Increase in tone height show repetition of notes: A, B, … , F, G
TONE CHROMA the same for notes w/ same letter,
same fundamental frequencies multiples of one another
Octave an interval A through G
o Pitch not determined by presence of fundamental frequency
but by info in it: such as spacing of the harmonics, the repetition
rate of the waveform that indicates the fundamental frequency
o EFFECT OF THE MISSING FUNDAMENTAL the constancy of pitch
even when the fundamental or other harmonics are removed
PERIODICITY PITCH the pitch we perceive in tones that has
had harmonics removed
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Document Summary

Ch11 sound, the auditory system and pitch perception. Sound two definitions, physical & perceptual: physical: sound is pressure changes in the air or other medium, perceptual: sound is the experience we have when we hear. Sound as pressure changes: sound stimulus occurs when an object"s movements/vibrations cause. Pressure changes: complex tones: complex tones waveform != a sine wave, but a combination. Is a periodic tone the waveform repeats. Repetition rate of complex tone is called the. Periodic complex tones consist of number of pure tones pressure changes in air, water, any elastic medium surrounding the object ex. loudspeaker vibrations affect surrounding air by: Condensation diaphragm moves out push air molecules: can build a complex tone by additive synthesis = number of sine- wave components are added together to create a complex tone. Fundamental frequency starting point for creating a together, increase nearby molecule density complex tone, the first pure tone. Rarefaction speaker diaphragm moves back in pull air.

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