Transcript Pitch Perception

Pitch Perception
• Or, what happens to the sound from the
air outside your head to your brain….
Sensitivity of the human ear:
•varies with pitch
•varies with loudness
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)
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)
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)
“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
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”
• 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
Absolute pitch can be a
negative:
• playing or singing in a key other than
written (transposed)
• Playing or singing in a group which
strays off pitch
• constant awareness of pitch labels hurts
enjoyment of music
“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
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 pitch:
1. When second pitch is close, most people
think the resultant sound is “consonant”
2. As second sound gets farther away, very
few people think sound is consonant
3. After two sounds get to around the distance
of a minor third, most people again think the
resultant sound is consonant
Perception of multiple tones
• When two pure tones are heard, one stays
the same and the second one can be varied
in pitch:
1. Very close  sounds like one tone, with
beats
2. After passing “limit of frequency
discrimination”  sounds like two tones with
“roughness”
3. After passing “critical band”  sounds like
two tones sounding smooth
• 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
• 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
• This supports the “place” theory of
response of the basilar membrane
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?)
Second order effects
• Beats created from two tones an octave
apart, mistuned slightly
• (try this with oscillators)
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
• 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
• Auditory system can perceive the overall
repetition rate of mixed sounds, which is the
frequency of the “missing” f0