Re: Granular synthesis and auditory segmentation (Jont Allen )

Subject: Re: Granular synthesis and auditory segmentation
From:    Jont Allen  <jba(at)RESEARCH.ATT.COM>
Date:    Thu, 22 Oct 1998 13:28:11 +0000

meijer(at)NATLAB.RESEARCH.PHILIPS.COM wrote: > > [BTW, for clarity of discussion: the following is about stationary > sounds only, where onsets, decay etc do not play a role, because > the discussion of temporal processing in non-stationary sounds is > worth a separate discussion, and things are already quite tricky > without involving non-stationary sound. I add this note because > the original subject of granular synthesis, and certainly my own > application of that, would normally deal with non-stationary sounds.] Are two tones that beat stationary or non-stationary, by your definition? > > I wrote (i.e., Peter Meijer) > > > I'd love to hear about *psychophysical* auditory perception > > experiments that unambiguously demonstrate temporal processing > > in humans in the 3 to 5 kHz range! My expectation is that such > > results have not been found... > > Jont Allen replied > > > I think this question needs some clarification. If you beat two > > tones at 10 kHz, say beat 10 and 10.05 kHz tones, you will hear > > the 50 HZ beat. This is clearly due to "temporal processing" > > above 5 kHz. > > I'll try to clarify: (neural) "temporal processing" above 5 kHz > is not needed for your example, because the mechanical filtering > and half-wave rectification of your 10 + 10.05 kHz tone gives a > strong 50 Hz component entering the auditory nerve. This 50 Hz > component can in fact be viewed as a demodulated envelope of the > original 10 + 10.05 kHz tone. The 50 Hz component is well within > regular neural bandwidth (we don't even need the "volley principle" > for that) and will most likely also be seen in the interspike > periodicities inside the auditory nerve, and it is well below the > 3 to 5 kHz range I was attempting to formulate my hypothesis for. I think the problem here is what you mean by "above 5 kHz." You are thinking of the demodulated signal components being above 5 kHz, rather than the input stimulus or filter output being above 5 kHz. This was what I was trying to draw out with my example. Now there are two reasons that the demodulated (neural) signal cannot have components above 5 kHz. First is the well known 4 kHz lowpass filtering of the synapse, that causes the loss of pure tone synchrony (Kiang monograph + Don Johnson PhD Thesis), and the second is the cochlear filter bandwidth which restricts the bandwidth of the rectified neural resp. In my opinion, even with the "volley principle" you cant process signals that have been removed by a filter, as in this case. The volley principle cant improve the SNR and recover the signal, since No processing can do that. > > In other words, I think the only "temporal processing" is here on > the 50 Hz accounted for by place theory and half-wave rectification: > no need for (neural) "temporal processing" above 5 kHz here. > > What I basically want to know is what the "volley principle" > nerve frequencies in the 3-5 kHz range bring us functionally, > if that helps to clarify what I am after. As I said above, you cannot recover signals that have been removed to less than the noise floor by filtering with the volley principle. I guess I am agreeing with your first statement, if modified such that you replace the 3-5 kHz range to say "above the frequency of the loss of pure-tone neural syncrony (i.e., 4 kHz): >> I'd love to hear about *psychophysical* auditory perception >> experiments that unambiguously demonstrate temporal processing >> in humans in the 3 to 5 kHz range! My expectation is that such >> results have not been found... > > Peter Cariani added > > > -- one can still make good octave judgments if the upper tone > > is at 3 kHz, but this becomes guesswork by the time one gets up > > to 5 kHz. I would guess that this is because the "hard lowpass syncrony cutoff" is at 4 kHz (at least in the cat. We dont have Human data on this point.) > > OK, I like this one. That *could* be a good argument to make > temporal processing up to 3 kHz plausible for explaining this > psychophysically observable effect, because one most likely > needs temporal periodicity information to obtain an absolute > reference for making an octave detectable as something "special". > (Within a filter bank an octave would not appear as special.) > > I checked Brian Moore's Psychology of Hearing again on this, > and even found (p. 209, 4th edition) a remark that ``octave > matches largely disappear above 5 kHz, the frequency at which > at which neural synchrony no longer appears to operate.'' > > ... > Best wishes, > > Peter Meijer > > Soundscapes from The vOICe - Seeing with your Ears! > > > McGill is running a new version of LISTSERV (1.8d on Windows NT). > Information is available on the WEB at -- Jont B. 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