pitch Flashcards
pitch
the “attribute of auditory sensation in terms of which sounds may be ordered on a musical scale” (ANSI, 1994)
frequency discrimination
How sensitive are you to changes in something, can you tell that its not the same as before? Rule: at 1000hz the freq different limen is about 2hz.
around .2-.3 of a %. need larger greq different to tell things apart.
limen
threshold for frequency
2 ways to determine pitch of pure tones
temporal code; place code
phase locking
you can see when the neuron fires in relation to the cycle of the stimulus. time tells you when spikes occur in relation to when the cycle began
Neurons are firing systematically. They’re sensitive to where you are in the waveform. When they’re firing its orderly.
temporal code
So if your neurons fire regularly and you can tell, then you can mentally figure out that THIS is the certain freq youre listening to.
You can use time (time between) the neural firings which will tell you the period of the cycle to calculate what the frequency actually is.
Synchrony index
how well the firings fit into 1 half of a cycle of a waveform.
The better the neuron is firing into that cycle, the better our index is.
harder to fire and reload for high freq
volley principle
safety net at 4kHz
as the freq increases, what youre doing is working with a # of diff fibers that are working together. Its phase locked, just not on every cycle.
Use info from multiple neurons to get phase lock info up to 4kHz
place code
von bekesy.
Basilar membrane is already encoding in diff freq, so lets pay attention to which is firing. If its this place, its higher freq than this place.
Think about auditory nerve position 1 firing at low freq and position 2 firing at high freq. we can tell theyre different freqs because of the position along the BM
Pure tones: Timing code vs Place code
low freq: timing AND place. High freq: place only.
Phase locking only for tones below 4 kHz.
Frequency difference threshold increases rapidly above 4 kHz.
Musical pitch absent above ~4 kHz (top of piano)
pitch of complex waveforms
most = periodic.
spectra has harmonics (integer multiples of the fundamental)
pitch of a complex periodic tone is close to the pitch of a sine wave @ fundamental
The pitch that you hear is the lowest component/fundament freq.
Place theory
Helmholtz; pitch is heard @ fundamental because fundamental freq is the highest level low-freq component; thus gives lowest freq peak on BM
Helmholtz hypothesis/prediction?
(Hypothesis) If the pitch of a complex waveform is heard at the fundamental because the fundamental frequency is the highest level low-frequency component and thus gives the lowest frequency peak on the basilar membrane…
(Prediction) Then, the pitch should change if the energy at the fundamental frequency is removed.
Seebeck’s siren
a place theory test.created a stimulus where the low freq component is gone and the new pitch should be 2/T. B and C should be the same pitch, but they’re not! A and C are.
Virtual pitch
pitch of the missing fundamental
distortion
Helmholtz (who favored place theory) countered Seebeck’s results by suggesting that the ear reintroduces energy at the fundamental by a process of distortion
not intended to be presented..just shows up!
how distortion works
Distortion 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. (explanation)
Evidence against place theory
Near threshold listening; masking; pitch shift
Virtual pitch: near threshold listening
high level sounds can produce distortion, where low level sounds dont.
(Hypothesis) If virtual pitch is heard because the ear reintroduces energy at the fundamental by a process of distortion…
(Prediction) Then, the pitch should disappear if the harmonics do not produce distortion.
Listeners can still detect a virtual pitch with low-level sounds, so virtual pitch cannot be attributed to distortion.
Virtual pitch: masking noise
(Hypothesis) If virtual pitch is heard because the ear reintroduces energy at the fundamental by a process of distortion…
(Prediction) Then, the pitch should disappear (or at least change) if the energy at the fundamental frequency is masked.
aka if distortion was generating this tone, then we couldn’t mask it.
Virtual pitch: pitch shift
(Hypothesis) If virtual pitch is heard because the ear reintroduces energy at the fundamental by a process of distortion…
(Prediction) Then, the pitch should remain constant so long as the frequency separation between the component tones remains constant
didn’t work. the pitch was shifting
temporal theory
Schouten (1941) proposed that the brain times the intervals between beats of unresolved harmonics of a complex sound, in order to find the pitch. pith is based on the period of the waveform.
evidence against temporal theory
dominant region; cross ear pitch
virtual pitch: dominance region
(Hypothesis) If virtual pitch is heard because the brain times the intervals between beats of unresolved harmonics of a complex sound
(Prediction) Then, unresolved harmonics should produce more salient pitch than resolved harmonics
virtual pitch dominance region experiment
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. dominance region should be at high freq (>~2khz), BUT the dominant region of pitch perception is 600-1400 where harmonics are resolved
virtual pitch: cross-ear pitch
(Hypothesis) If virtual pitch is heard because the brain times the intervals between beats of unresolved harmonics of a complex sound
(Prediction) Then, there should be no virtual pitch if consecutive frequency components go to opposite ears.
place 1 tone in each ear and theyre in isolation because they’re in different filters because theyre in diff ears. listeners could still hear a virtual pitch! means dont need to interact temporally in the cochlea. (no distortion)
pattern recognition theory
if not place/temporal theory, then what is it?
Goldstein’s theory states that pitch is determined by a pattern recognition process on the resolved harmonics from both ears.
The brain finds the best-fitting harmonic series to the resolved frequencies, and takes its fundamental as the pitch.
