Re: Can a timbre affected by a shifted virtual pitch evoked by double-spaced harmonics?

[Martin Braun <nombraun@xxxxxxxxx>]

Chen-Gia Tsai wrote:

> I have used a program (see
>http://www.dcs.shef.ac.uk/~martin/MAD/auto/auto.htm ) and seen that the
>shifted virtual pitches evoked by inharmonic components are precisely
>predicted.

>This success of autocorrelation in modeling pitch extraction is, at least
>for me, very impressive.

Chen-gia, it does not help, if something is predicted by a model, but not
heard by human ears. Your sound files showed that the "predicted" pitches
did not match the pseudo-pitches of your examples.

As to the pitch model of autocorrelation, also this is a model that is
anatomically and physiologically unrealistic. Ray Meddis, one of the major
advocates of this model has now given it up, in favor of a new model (see
below) that is based on anatomical and physiological data that were
described in detail by Gerald Langner and me.

[By the way, the term "virtual pitch" should no longer be used, because
pitch is real, and "virtual", an extremely "fuzzy" term from the beginning,
has in recent years gained a new meaning in IT contexts. Of the 1077
abstracts of the presentations at the current ARO meeting only one still
uses this old term.]

You are lucky that at this year's ARO meeting, which has started today, two
presentations explicitly deal with your issue. Here are the two abstracts:

[300]
Pitch Shifts For Unresolved Complex Tones And The Implications For Models Of
Pitch Perception

*Rebecca Kensey Watkinson, Christopher John Plack
Department of Psychology, University of Essex, Colchester, United Kingdom

This experiment compared the pitches of complex tones consisting of
unresolved harmonics with fundamental frequencies (F0s) of 100, 125,
166.67, and 250 Hz. The complexes were bandpass-filtered between the
22nd and the 30th harmonic to produce a set of unresolved harmonics
with distinct envelope peaks ("pitch pulses"). Each tone burst had a
duration of 5 waveform cycles and two tone bursts were presented
consecutively, separated by a brief gap of either 0, 1, or 2 waveform
periods. The envelope phase of the second tone burst in each pair was
advanced or delayed by 0.25, 0.5, or 0.75 periods. Effectively, this
resulted in a variation in the inter-pulse interval (IPI) between the two
tone bursts. A no-shift control was also included, in which the IPI was
fixed at an integer number of periods. Pitch matches were obtained by
varying the F0 of a comparison complex tone with the same temporal
parameters as the standard, but without the phase shift. Relative to the
no-shift control, the variations in IPI produced substantial pitch shifts
when there was no gap between the bursts, but no effect was seen for
gaps of 1 or 2 periods. This is consistent with a pitch mechanism
employing a long integration time for continuous stimuli that is reset in
response to temporal discontinuities of greater than 1 period of the
waveform. The results were inconsistent with the autocorrelation model
of Meddis and O'Mard (1997), but a modification of the weighted
mean-rate model of Carlyon et al. (2002) could account for the data.


[376]
A Model of the Physiological basis of Pitch Perception.

*Raymond Meddis
Psychology, University of Essex, Colchester, United Kingdom

Little is known about how pitch is processed by the auditory nervous
system. Autocorrelation models of pitch extraction have been successful
in simulating a large number of psychophysical results in this area but
there is little support for the idea that the nervous system acts as an
explicit autocorrelation device. To address this issue, this poster
presents a design for a new model of pitch perception based upon
known neural architecture and also presents some preliminary pitch
analyses using the model. The model offers a physiologically plausible
system for periodicity coding that avoids the need for long delay lines
required by autocorrelation. The system incorporates a model of the
human auditory periphery including outer/middle ear transfer
characteristics, nonlinear frequency analysis and mechanical-electrical
transduction by inner hair cells. The resulting 'auditory nerve' spike
train is used as the input to three further stages of signal processing
thought to be located in the cochlear nucleus, central nucleus and the
external cortex of the inferior colliculus, respectively. The complete
model is implemented using DSAM, a development system for auditory
modelling. The output from the system is the activity of a single array
of neurons each sensitive to different periodicities. The pattern of
activity across this array is uniquely related to the fundamental
frequency of a harmonic complex. The testing of the model is still in its
early stages but has so far been successfully tested using a range of
harmonic stimuli and iterated ripple noise stimuli. The poster will report
on current progress in testing and refining the model.

Martin

-------------------------------------------
Martin Braun
Neuroscience of Music
S-671 95 Klassbol
Sweden
e-mail: nombraun@telia.com
web site: http://w1.570.telia.com/~u57011259/index.htm