Coclear vs. psychoacoustic models (=?iso-8859-1?Q?Lars_Bramsl=F8w?= )

Subject: Coclear vs. psychoacoustic models
From:    =?iso-8859-1?Q?Lars_Bramsl=F8w?=  <LBRAMSLOW(at)BK.DK>
Date:    Tue, 19 Aug 1997 18:53:00 +0200

Dear Jont + List, A few belated replies to your comments, received july 11: > Isn't it also important to simulate recruitment and > the variation, if any, of the critical ratio with level? Simulation of recruitment and critical ratio with level was dealt with in the model, indirectly. The roex-filters were widened according to level, giving loudness recruiment and reduced frequency selectivity. Critical ratio is a result of 1) frequency selectivity, which was simulated and 2) what Glasberg and Moore term 'detection efficiency', i.e. at what S/N ratiowithin the band the tone is audible. Zwicker terms this 'Schwellenfaktor'. This 2nd factor was not modified, if that's your question. > What about Fletcher and Munson's 1933 loudness model paper, > Munson and Gardner's 1950 forward masking loudness model paper, and > Steinberg and Gardner's 1937 model of recruitment? > These give ample information to do what you want, dont they? I don't know. I have not consulted those papers during the model work, as I wasn't aware of them. > I guess I still dont know the difference between an ERB and a critical band. > Can somebody help me? The concept of the bark and the ERB scale is the same, however based on the roex-filter model, the ERB scale has more bands, roughly 32 in the range 100 - 10 kHz. There are 22 critical bands in the same range. The ERB bandwidth is ERB(Hz) = 24.7(4.37*fc(kHz) + 1), thus the bandwidth minimum is 35 Hz (Critical band is 100 Hz) and the high-frequency bandwidth is roughly 10% of the centre frequency (Critical band is appr. 20 %). This is just the short version, others may fill in. > This is an excellent starting point if you are trying to make > objective measures as applied to hearing aids. If you want to > model the cochlea, this model doesn't help much. No, of course not! That wasn't the intention either. > This is the data that was used to set the parameters of this > model. I should hope that it would do a good job. It sounds simple, but it isn't, when the complete model is re-used to predict its design data, since the roex-model was combined with a mix of outer-ear corrections and the Zwicker loudness growth function. > Are you saying that the cochlear models dont work in real life? Not for this type of task. As I recall Jim Kates made a cochlear model with hearing loss with percentage loss of inner and outer hair cells, but the catch is to specify these percentages correctly to simulate the psychoacoustic performance of a patient. Do you have any counter-examples? Lars Bramslow responds: > What problem are you trying to solve? Do you want to build a > model of the auditory system, or make a new hearing aid? > I sure didnt try to build a better cochlear model while working > on a hearing aid design, I was too busy. I was applying a model of the auditory system for the purpose of predicting subjective quality. There was no hearing aid design involved whatsoever, despite the affiliation with a hearing aid company. I was quite busy doing listening tests, auditory modeling, statistical analysis, data fitting etc! > The basic research in how the cochlea and auditory system works > is a difficult puzzle. We do not all agree on how it works. > But without differing opinions, we cannot make progress. > The purpose of a cochlear model is to obtain a basic understanding of > what is going on, not provide a simulation that can be used to > simulate a hearing aid. > The Cambridge (Moore et al.) model is based on Zwicker. The Zwicker model > is based on Fletcher and Munson (1933). As far as I can tell, the > Fletcher and Munson model is based on Wegel and Lane (1928). > The user of a model should not try to "compete" with the designer > of a good cochlear model, nor should the modeler try to compete > with the hearing aid designer. Each has an important place, and > plays a role. I agree! The coupling between hearing aid design and more basic research was absent in my project, just as intended. I do think, as previously stated, that the published cochlear models are of limited PRACTICAL use, but this does not make them less significant as research tools. Regards, Lars Bramslow, August 19, 1997

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