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Re: effect of phase on pitch
Bert Schouten <Bert.Schouten@LET.RUU.NL> writes:
>Perceptual effects of phase on pitch or timbre could be epiphenomena
>of a mechanism needed for sound localization. We need some form of
>phase-locking in the auditory nerve in order to be able to compare
>the signals from the two ears. In natural environments the ear
>receives no phase information about the sound source, so pitch and
>timbre cannot normally be based on temporal information, but the
>sensitivity to temporal differences between the two ears may
>influence pitch or timbre whenever headphones are used or when
>phones are inserted into animals' ear canals.
This argument seems almost right, although I'd add that phase
information is highly predictive of self-motion. Thus there may
be a strong localization component of phase both for objects and
for self-location within the frame of reference. Similarly, phase
change is correlated with object acceleration within an environment.
If an sound source starts to move toward the listener and there is
a reflecting wall behind the sound source, both the sound source
acceleration and the acceleration of the source relative to the
wall would be predictable from the phase changes of the direct and
the reflected sound.
There is some research (see Stoffrengen's recent paper for an
overview) into perception of self motion through auditory cues.
I argue that a large proportion of that information is contained
in phase. However, if we are to maintain Pitch Constancy (similar
to color constancy) for moving objects, phase changes must be
removed from the perception of pitch and relegated to motion
detection. There is some error in this process. The error can be
most readily seen in an environment where the subject is wearing
headphones, because then the phase changes are decoupled from the
other sensory modes of information about self-motion. It is partly
this multi-modal self motion information that allows the phase
information to be removed from the incoming auditory signal and
pitch constancy to be attained.
Steven M. Boker 219-631-4941 (office)
email@example.com 219-631-8883 (fax)
http://www.nd.edu/~sboker 219-257-2956 (home)
Dept. of Psychology, University of Notre Dame, Notre Dame, IN 46556