Re: Granular synthesis and auditory segmentation ("Richard J. Fabbri" )

Subject: Re: Granular synthesis and auditory segmentation
From:    "Richard J. Fabbri"  <fabbri(at)NETAXIS.COM>
Date:    Thu, 15 Oct 1998 17:30:34 -0400

Peter,

>[I say "roughly reflect", because half-wave rectification
>does subtly alter the form of interspike interval
>distributions and autocorrelation functions.
>The autocorrelation of a sinusoidal component has the
>form of a cosine of the same frequency; the autocorrelation
>of a half-wave rectified component has flattened troughs,
>but closely resembles that of the unrectified component
>near the peaks. The positions of peaks and troughs are
>unchanged by half-wave rectification. When you listen to
>a half-wave rectified pure tone, it does sound very
>slightly different in timbre, slightly buzzy, but the
>pitch is the same,so the pure tone and its rectified
>counterpart don't sound all that different. I think
>Didier is right, however, in insisting on factoring
>in the effects of cochlear filtering first -- there
>are simple thought experiments with waveforms having
>positive-negative asymmetries which nevertheless still
>sound the same when polarities are reversed. If we
>only listened to the positive parts of asymmetric
>waveforms, different polarities should sound different.]

        ... Didier's example of listening to a Halfwave Sine vs a Sine is
        not equivalent to the transduction function provided by the
        neural HALFwave action caused by a neural refractory period
        when the acoustic waveform is of the opposite polarity.

        ... Basically, the Basilar/Tectonic membranes are mechanically
        driven by the BIPOLAR Sine waveform which is THEN HALFwave
        transduced WHILE the Inner Hair Cells undergo the FULLwave
        mechanical motion of a FULLwave sinewave.

        ... This is NOT the same thing as providing a HALFwave
        ACOUSTIC waveform as THAT sets-up a QUITE different
        quiescent base-line (+/-) reference for the Basilar Membrane
        than does a SINE wave.
        ... i.e., the EFFECT is HALFwave transduction into neural pulse
        rates while the transduced mechanical MOTION is FULLwave.


Regards,
Rich Fabbri

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