Pitch Perception

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Pitch Perception

• Or, what happens to the sound from the air
  outside your head to your brain.

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• Sensitivity of the human ear
• varies with pitch
• varies with loudness

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Perception of one pitch

• Most sensitive around 3000 Hz.
• Least sensitive at high and low ends
• High frequency sensitivity decreases with age
  (and damage to ear)

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Frequencies important for music

• Frequency range of piano 27.5-4224 Hz.
• Frequency range of voice fundamentals low C
  for bass - 65 Hz. high F for soprano - 1397
  Hz.(important overtones are higher)

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Pitch is determined by hair cells on basilar
membrane

• 2/3 of basilar membrane accounts for range of
  100-4000 Hz.
• Membrane has a logarithmic scale jump of one
  octave anywhere in range is about the same jump
  on membrane (3.5-4 mm)

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Just Noticable Difference

• When presented with two tones in succession, when
  are they the same and when are they different?
• Slow change detection of .5 at 2000 Hz. (only
  10 Hz.!)1 at 350 Hz.3 at 100 Hz.(Try this
  with oscillator)
• Fast change much more sensitive

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Absolute pitch(also known as perfect pitch)

• Ability to identify the note name of a sound, or
  to reproduce a specific note, without reference
  to an external standard.
• The above skill sometimes called tone AP, where
  the skill to recognize whether a piece of music
  is played in the correct key is piece AP

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• One person in 10,000 claims to have it
• Absolute pitch is not necessarily perfect
  people can identify 70-100 of midrange tones
  (chance level is 1/12 or 8.3)
• Develops during early life nature vs. nurture
  source hard to determine
• Composers with AP include Mozart, Scriabin,
  Messiaen, Boulez
• AP can be a negative playing or singing in a key
  other than written or in a group which strays off
  pitch constant awareness of pitch labels hurts
  enjoyment of music

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• Relative pitch ability of musicians to
  determine note name with external standard
  present
• This is an expected skill for trained musicians
  some will be better than others

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Perception of multiple tones, related to
consonance

• When two pure tones are heard, one stays the same
  and the second one can be varied in pitch1.
  When second pitch is close, most people think the
  resultant sound is consonant2. As second sound
  gets farther away, very few people think sound is
  consonant3. After two sounds get to around the
  distance of a minor third, most people again
  think the resultant sound is consonant

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Perception of multiple tones

• When two pure tones are heard, one stays the same
  and the second one can be varied in pitch1.
  Very close ? sounds like one tone, with beats2.
  After passing limit of frequency discrimination
  ? sounds like two tones with roughness 3.
  After passing critical band ? sounds like two
  tones sounding smooth

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• These effects depend on how high the tones are
• Phenomenon is true for both tones heard by one or
  two ears
• When 2 tones are separated and fed into different
  ears, roughness disappears

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• We infer that effect comes from each tone
  exciting a range on the basilar membrane (not
  one single point), and that the two tones
  interfere with each other

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Combination Tones

• Heard from two tones of strong intensity
• Difference tone is f2-f1
• When two tones are a fifth apart, the difference
  tone is 1 octave below f1
• Other tones made from 2f1-f2 and 3f1-2f2
• Thought to come from nonlinear distortion of
  the primary wave form stimulus in cochlea - the
  vibration of the additional tone is present in
  cochlea
• (try with 2 oscillators?)

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Second order effects

• Beats created from two tones an octave apart,
  mistuned slightly
• (try this with oscillators)

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Fundamental tracking

• The processing system supplies the missing
  fundamental from a set of upper harmonics
• Example two tones a fifth apart ? another note
  heard 1 octave below f1
• Two tones a third apart ? another note heard 2
  octaves below f1
• The result is the same as difference tone but is
  not the same phenomenon vibration of additional
  tone is not present in the cochlea

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• What is happening here?? Fundamental tracking is
  shown to happen even when pitches are fed into
  separate ears
• The pitch perception process is so used to
  hearing complex tones with a fundamental and
  upper overtones (from harmonic series) that if it
  only hears some of the overtones, it supplies the
  fundamental

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• Auditory system can perceive the overall
  repetition rate of mixed sounds, which is the
  frequency of the missing f0