(Eckard Blumschein )

From:    Eckard Blumschein  <Eckard.Blumschein(at)E-TECHNIK.UNI-MAGDEBURG.DE>
Date:    Thu, 8 Mar 2001 11:38:21 +0100

Dear Ramdas Kumaresan, On Wed, 07 Mar 2001 you wrote: >I agree with the general tone of your postings. I have expressed similar >sentiments in my original posting (analog delay line vs 'continuously >distributed memory'). However, IMO, 'the signal is not simply >transformed at all' is not true. After all the cochlea does have >resonant structures and hence does some form of filtering (which is >convolution with damped sinewaves, i.e. a form of weighted Fourier >transform.) I would like to fall into your third category. This was my third category: >>Hopefully, at least a few people will be able and willing to attack the >>problems the other way round, that is, based on what is already >>functionally understood, fairly regardless of the traditional approach and >>the high level of sophistication in mathematics. Well, I feel we are close. When I wrote 'not simply transformed at all', I tried to object against the illusive hope that something like the Fourier transform will be suited to actually mimic the function of cochlea. Look at David McGrath's solution (US Pat. 5,502,747) to the comparable easy problem of building a FIR-HRTF filter. It consists of a first time-domain low-latency filter and a number of FFT fast-convolution filters. Dolby headphones are based on this rather cochlea-lookalike structure. About simultaneously (in 1995) William Gardner of MIT proposed in JAES nearly the same hybrid structure as to compensate for the reverberation delay. Neither digital time-domain filters nor fast-convolution filters are optimal in real-time operation. The fast-convolution filters are not fast enough. You are certainly also aware of acausality with frequency-domain filtering. Narrowing my mind to the horizon set by tools like digital signal processing and mathematical analysis, I would not be able for unbiased understanding of what is going on. That's why I am pointing my finger squarely to what I consider a fundamental difference between the presumed function of the inner ear including pre-selection, amplification and adjustment over a huge dynamic range, preparation for robustness and adaptation to massively parallel processing on one side, and any mutilated feet of Cinderella's sisters on the other side. I am convinced: Any straightforward blind mathematical approach is doomed to fail. Any convenient simple transform from time domain into any mathematical construct will not adequately fit the function of hearing. As soon as we were or will be able to largely understand auditory function, we tried or will try inventing something that fits roughly or more reasonably, respectively. Cheers, Eckard

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