Pitch

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Pitch

• Lecture 6

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Definition of pitch

• Perceptual attribute of frequency
• ANSI attribute of auditory sensation inwhich
  sounds may be ordered on a scalefrom low to high

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Over what frequency range is pitch perceived?
30 Hz
5 kHz
12 kHz
Pitch perception range
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Mechanisms of pitch coding for pure tones
(rate-) place theory

• A single frequency excites one region of the BM

Inner ear performs spectral analysis. The
different excitation patterns are what code
pitch. Neurons getting maximal stimulation (i.e.,
near the peak of the excitation pattern) will
fire fastest Probably how we detect pitch changes
at higher frequencies (which are too high for
phase locking)
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Mechanisms of pitch coding for pure tones
temporal theory
Pitch depends on timing of neural impulses (phase
locking) We cant phase lock at higher
frequencies. We can detect differences in tones
that are probably similar in excitation pattern
(i.e., that pitch difference isnt explained by
the place theory). So, phase locking may be the
primary mechanism at low frequencies
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Pitch coding for complex tones

• Take a complex signal such as a series of
  harmonics (100, 200, 300, 400 Hz) and pass it
  through the auditory filterbank
• The lower freq. filters are narrower
• Those centered on a harmonic have high output
• Those centered between harmonics have low output
• The ear can resolve lower freq. harmonics
• At higher freqs, filters are wider pass energy
  from several harmonics so the filter output is
  high whether centered on a harmonic or not
• Higher freq. harmonics cannot be resolved

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Pitch of complex tones using the resolved
harmonics

• Pitch is dictated by resolved harmonics
• In addition to auditory filter (place), you can
  also have phase locking to the lower harmonics
• The auditory system uses the lower harmonics to
  determine the fundamental (pattern recognition)

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Missing fundamental

• BUT
• Even with the fundamental removed (or masked),
  there is still an audible pitch related to the
  fundamental frequency, the residue pitch or
  missing fundamental

500 Hz
.5 1 kHz
.5, 1, 1.5, 2 k
1, 1.5, 2 kHz
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Pattern recognition

• How does the auditory system figure out the
  fundamental from the (resolved) harmonics?
• The distance between the harmonics is the same as
  the fundamental, e.g.,
• 100 Hz fo 200, 300, 400, 500.
• 250 Hz fo 500, 750, 1000, 1250
• The system matches the pattern to its
  fundamental (somehow)

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Pitch from unresolved harmonics of a complex tone

• Higher harmonics passing through the same filter
  interact, causing beats at the output of the
  filter. They beat at the fundamental
• Neurons can phase lock to envelope of the beats

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Timbre

• (not covered in your book but relevant to
  pitch)
• Def the attribute of auditory sensation in
  terms of which a listener can judge that two
  steady complex tones having the same loudness,
  pitch and duration are dissimilar (Plomp,1970)
• Timbre is multidimensional and subjective
• Timbre is affected by
• Spectrum
• Temporal envelope
• Periodic vs. nonperiodic/irregular waveforms
  etc.

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Example of timbre
Fo ?
Fo ?
http//physics.mtsu.edu/wmr/four_5a.htm