>the human hearing system is kind of an LTI... only at very low level >processing. The consistency of measured signal (= perceiving the same >signal the same way at all time as somebody wrote here) is present in >the ear canal up to brainstem -> inferior colliculus.
My understanding is that there are measurable nonlinear effects even in the cochlea. Apparently when a loud frequency is present that excites one region of the membrane, the surrounding fibers react to dampen nearby sound and reinforce the purity of the dominant frequency. The pithy way of phrasing this is "the frequency response of the ear of a dead cat is different from that of a live cat." Not sure if anybody actually did that exact experiment to verify that... Of course, that doesn't invalidate the "same sound sounds the same later" property, but if you ask me that's a much much broader thing than LTI. For example, any static nonlinearity - no matter how extreme and nonlinear - will always produce the same output given the same input. That doesn't mean it's linear, it just means it's time-invariant. E E On Wed, May 7, 2014 at 10:59 PM, Enr G <e.glerean....@gmail.com> wrote: > My two cents as a person in the field: > > the human hearing system is kind of an LTI... only at very low level > processing. The consistency of measured signal (= perceiving the same > signal the same way at all time as somebody wrote here) is present in > the ear canal up to brainstem -> inferior colliculus. But once we go > to higher neuronal processing of auditory signals things get > complicated and the same signal can be perceived in many different > ways (e.g. google for top-down mechanism of auditory attention). The > (non linear) fourier analysis and interpreting sounds as sinusoid are > valid at ear canal level, and there are models with filterbanks to > simulate that. But once we go to conscious perception (=cerebral > cortex) evidence from animal research seems to point to a more complex > analysis performed by the neurons: the so called spectro-temporal > modulation (basically a 2D fourier transform). I.e. envelopes and > phases are treated in different ways to identify "sound objects". For > those interested, this is a nice starting point (open access): > > http://www.ploscompbiol.org/article/info%3Adoi%2F10.1371%2Fjournal.pcbi.1003412#pcbi-1003412-g007 > > e. > > On Thu, May 8, 2014 at 8:28 AM, eric <ericzh...@gmail.com> wrote: > > It would appear to me that the human hearing system is an LTI system. > It doesn't react in a linear fashion to frequency or loudness, but it > perceives the same signal the same way at all times, disregarding aging, > hearing loss, etc. > > > > On 5/8/2014 1:25:28 AM, Sampo Syreeni <de...@iki.fi>wrote: > > On 2014-05-08, robert bristow-johnson wrote: > > > >> there was a way that you could do "subtractive dither" in that the > >> dither that you added before quantizing to a short word could be > >> subtracted (to regain 4.77 dB) [...] > > > > I have some code for just that, even, and even better ideas. Maybe I > > even mentioned them somewhere a while back? If not, will fully share > > given interest. (The code is rather shitty, and even the ideas would > > benefit from development. But still better than you see implemented > > anywhere.) > > > > Yet why-oh-why doesn't anybody just pop up their Audacity and a few > > megabytes of randomness, the way I originally asked? Because the stuff > > I'm talking about really is kind of interesting and unexpected, once you > > try it out on your own ears... > > > >> when you loop the noise, is it a "butt-splice"? (i.e. no crossfade.) > > > > Yes. Otherwise the splice might introduce an interpolation artifact > > which would invalidate the experiment from the start. > > > >> it's news to me that human hearing is LTI. > > > > Yes, well, it ain't. But even conventional psychophysical theory treats > > it as such. For example, why would we hear frequencies unless the ear > > was LTI? Fourier analysis, that is sinusoids as something special, > > doesn't make much sense unless you assume... Well, you know, at least > > something having to do with linearity and shift-variance... ;) > > -- > > Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front > > +358-40-3255353, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 > > -- > > dupswapdrop -- the music-dsp mailing list and website: > > subscription info, FAQ, source code archive, list archive, book reviews, > dsp links > > http://music.columbia.edu/cmc/music-dsp > > http://music.columbia.edu/mailman/listinfo/music-dsp > > > > > > --- > > This email is free from viruses and malware because avast! 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