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Psychoacoustics Final > Pitch > Flashcards

Pitch Flashcards

1
Q

What is Pitch?

A

part of a sound that makes you able to organize it on a musical scale
part of auditory sensation associated musical melodies

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2
Q

Range of Pitch in Frequency

A

From 30 - 4500 Hz
Piano ranges from 27.5 Hz to 4200 Hz
Above 5000 Hz something is different between frequencies but no longer a musical aspect to it

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3
Q

DL or JND

A

Difference Limen or Just Noticeable Difference

  • dependent on frequency, sound level, duration of tone, & suddenness of frequency change
  • need to be at least this far apart to tell the difference
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4
Q

Human frequency discrimination vs piano keys

A

We hear frequency changes far better than the difference between piano keys - you could put another 29 keys in between

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5
Q

What is the Frequency Difference Limen at 1000 Hz?

A

2 Hz

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6
Q

Frequency Discrimination

A
  • measured in % of frequency (graph x: frequency (kHz), y: Frequency difference Limen (%)
  • starts to go way higher at 4000 Hz
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7
Q

Phase Locking

A
  • looking at the time of the neuron firing
  • look at each cycle separately and plot when the neuron fired - compared to the start of each cycle
  • plot in a histogram to be able to see at what time each happened - usually
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8
Q

Where does phase locking occur most often?

A

The first half of the cycle (above the line) very few happen after that

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9
Q

What about phase locking helps in pitch discrimination?

A
  • The phase will change as frequency changes, relatively small changes in phase
  • You will have a spike every so often
    If phase locked – firing at the same point in each phase
  • use the time in between each neural firing to calculate what the frequency is
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10
Q

Phase Locking Limit

A
  • starts dropping off above 1000 Hz
  • lower frequencies are really good at phase locking (longer wavelength), higher frequencies are moving to fast so it’s hard to keep the neurons as locked in place and they don’t have enough time to recover/fire again
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11
Q

Volley Theory

A
  • many neurons are firing together, if you look at them individually they aren’t phase locked at higher frequencies because they can’t keep up BUT if you look at the group that is firing together they are phase locked together in groups
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12
Q

Place Code Theory

A
  • peak vibrations along different positions along the basilar membrane - unrolled cochlea looks like filters
  • Basilar membrane is already encoding, pay attention to which neuron is firing at the time, this place is a higher tone than that place
  • better for over 4000 Hz
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13
Q

Pure Tones: Timing Vs Place Theory

A

Low freq - timing and place
High freq - place only
- phase locking for tones below 4000 Hz
- frequency difference threshold increases rapidly above 4000 Hz
-musical pitch is absent above about 4000 Hz

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14
Q

Pitch of Complex Waveforms

A
  • All subjective no right or wrong answer
  • periodic
  • spectra consist of harmonics that are integer multiples of the fundamental
  • similar to pitch of a sine wave at the fundamental
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15
Q

Place Theory - Complex Waveforms

A
  • Helmholtz: pitch of a complex waveform is heard at the fundamental, because it is the highest level low frequency components (peak on basilar membrane)
  • SO if you take away the fundamental, the pitch should change
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16
Q

Seebeck’s test of Helmholtz, place theory

A
  • disk with wholes in it, spins around and air shoots through the holes
  • moves second hole to a new position, this makes the wave form more complex (you speed them up and combine into one tone)
  • doesn’t change the pitch! (should have because he removed the first harmonic/fundamental frequency)
    =virtual pitch, missing fundamental
17
Q

distortion

A

Helmholtz reaction to seebeck

  • the ear recreates the fundamental because it knows it’s been removed/should be there
  • produces energy at frequencies corresponding to the difference between two components physically present (i.e. at the harmonic spacing)
  • any pair of adjacent harmonics would generate energy at the fundamental
18
Q

Evaluation of Pitch Theories

A

Against Place Theory:

  • near threshold listening
  • masking
  • pitch shift
19
Q

Near Threshold Listening - Test of Virtual Pitch

A
  • high level sounds produce distortion, low levels don’t
  • low level, even the harmonics shouldn’t produce distortion
  • STILL hear the same pitch, so it isn’t caused by distortion
20
Q

Masking Noise - Test of Virtual Pitch

A
  • if the ear is reintroduces energy at fundamental by distortion - the pitch should disappear (or change) if energy at fundamental frequency is masked with a low pass noise (masking fundamental but not the remaining harmonics)
  • when low pass noise masker, wiped away pure tone, all masker
  • high pass noise used as a ‘reality check’ ???
  • telephones, actually 300-3000Hz, human speech actually 100-300, so distortion allows you to, your brain is filling in to tell the difference of peoples voices
21
Q

Pitch Shift - Virtual Pitch

A
  • if virtual pitch is heard because the ear reintroduces energy at fundamental by distortion - the pitch should remain constant so long as the frequency separation between the component tones remains constant
  • A: 800, 1000, 1200 Hz
  • B: 900, 1100, 1300 Hz
    • in these tests, should hear 200 Hz tone in each because that would be the fundamental breakdown of each
  • we know that distortion is the difference in frequency range - should both produce a pitch at 1000
  • SO distortion should stay the same even when the frequency moves because they have the same fundamental?
  • strong evidence that it isn’t distortion - but don’t know what it is…
22
Q

Evaluation of Pitch Theories - What are the evidence against place theory?

A

Near Threshold Listening
Masking
Pitch Shift

– if not place theory, then what?

23
Q

Pitch of Complex waveforms: Temporal Theory? (Hypothesis/Idea)

A

The brain times the intervals between beats of unresolved harmonics of a complex sound, in order to find the pitch

  • maybe it’s all about timing, looking at the waveform instead
  • excitation pattern: when you go up in frequency the filters are over lapping more and more, this is about the same for masking pattern essentially
  • how many filters is that tone going to effect, primarily letting in the one, but also some of the ones next door
  • everything “temporal” is telling your brain that things are happening in a certain way in time
24
Q

According to temporal theory, pitch is based on the period of the waveform

A
  • you should see based on frequency that certain harmonics should have the same pitch because of the temporal changes the periodic element is going from
25
Q

Total Evaluation of Pitch Theories

A 
Evidence again Place Theory: 
- Near Threshold Listening 
- Masking 
- Pitch Shift 
Evidence against Temporal Theory: 
- Dominant Region 
- Cross-ear Pitch
26
Q

Virtual Pitch - Dominance Region

A
  • Hyp: if virtual pitch is heard because the brain times the intervals between beats of unresolved harmonics of a complex sound…
  • (pred) then, unresolved harmonics should produce more salient pitch than resolved harmonics
  • unresolved harmonics beat together, this happens at higher frequencies, letting in sounds from next door filters
  • changes in the frequency of components in the dominant region influence the pitch of a complex sound more strongly than in any other frequency region
27
Q

According to Temporal Theory - Dominance should be…

A

region should be at relatively high frequencies (2000Hz where harmonics are unresolved) because the temporal information is clearest there
- BUT dominant region of pitch perception is 600-1400 Hz, where the harmonics ARE resolved.
- these carry the most information -> against temporal theory
(RESOLVED - ONE HARMONIC OR COMPONENT PER FILTER
- according to temporal theory, you have multiple components and they are coming through the same filter, beating against each other

28
Q

Virtual Pitch: Cross-ear Pitch

A
  • Hyp: if virtual pitch is heard because the brain times the intervals between beats of unresolved harmonics of a complex sound…
    -Pred: then, there should be no virtual pitch if consecutive frequency components go to opposite ears
  • one component in one ear, one in the other, nothing to beat against because they are in opposite ears
    Example:
    – left 1000 Hz, right 1200 Hz -> still have virtual pitch, doesn’t have to meet in the cochlea, goes against both theories & against distortion
29
Q

Pitch of complex waveforms: Pattern recognition Theory

A
  • pitch is determined by a pattern recognition process on the resolved harmonics from both ears
  • brain finds the best-fitting harmonic series to the resolved frequencies, and takes its fundamental as the pitch
  • *this is what we think today - brain is calculating what you are actually hearing
30
Q

Pitch Processor:

A
  • first estimates frequencies of individual components of a complex sound, such as 300, 400, 500 Hz
  • then notes that these frequencies could be produced by fundamental 100 Hz
  • look back at information, process and decide based on templates you have for patterns from different fundamentals this is a good match for 100 Hz template, bad for 110 Hz)
31
Q

Pitch Paradox

A

Shepard Scale
complex tones, each composed of 10 partials separated by octave intervals
ever ascending scale

Psychoacoustics Final (5 decks)

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