Re: granular synthesis and auditory segmentation ("John K. Bates" )

Subject: Re: granular synthesis and auditory segmentation
From:    "John K. Bates"  <jkbates(at)COMPUTER.NET>
Date:    Thu, 29 Oct 1998 17:17:54 -0500

Dear List, On Oct. 16, responding to my posting, Peter Cariani wrote: >If I understand your processing correctly, you retain some constant >proportion of successive half-waves, so that there is still a great deal >of correlation structure between the half-waves that retains most of >what is important to the auditory system. Yes. The half-wave/granular way of looking at a signal waveform lets you sort out and store interleaved granules from different sources and to capture ten-microsecond time differences and rapid sequence transitions. Granules avoid the limitations of the spectral window while carrying enough information to sort them into meaningful categories. Sources are associated with their granules by identifying their categories and relative times of arrival. Correlation recovers the information in temporal patterns of both tonal (periodic) and atonal (timbre) of each of the intermixed time/space signal sources. >When you have a receptor system that phase-locks to the stimulus, then >the timings of discharges will more or less faithfully replicate the >time structure of your half-waves, and the all-order intervals that >are produced will more or less look like the autocorrelation of your >half-waves. Phase locking might be a way the ear correlates half-wave arrival times with time-sequential events that carry meaningful patterns. >In the correlational view, having all of those >tuned filters makes the system much more robust >in the face of background noise and multiple >competing auditory objects. Here is an interesting point. From the ear's point of view, is there a solid definition of what constitutes background noise? Is there a difference between background noise and multiple competing auditory objects? If a noise-free environment is one that is devoid of acoustic sources then we must be talking about, say, tinnitus. If background noise is composed of multiple auditory objects, then by what process does the ear choose which background object is to be the "signal?" >A full-blown autocorrelation-based theory of speech coding is possible >that describes periodic and aperiodic speech sounds in terms of >running autocorrelation structure. I think that this kind of >theory would provide a way of thinking about some of the neural >correlates of your experiments in granular synthesis. I agree, especially since what I've been doing uses a modified running autocorrelator with ensemble-averaging referenced to the onset of each arriving granule. Regards, John Bates McGill is running a new version of LISTSERV (1.8d on Windows NT). Information is available on the WEB at

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