It may be fine to think of the ear as doing a Fourier transform as a first, crude approximation. For a more accurate description however, some nonlinear effects would have to be considered. And some of this already happens in the ear. As for hearing being LTI, think about forward and backward masking. Although it happens at a rather short time scale, it implies that time invariance is not always the case. Harmonic distortion and intermodulation of two sinusoids played loudly enough also speaks against linearity. I haven't tried the experiment, but I recall a composer collegue once complaining about repetition in the noise generator of Csound. I think they used a random generator with period 2^16 in those days, but it's been improved now. Risto Holopainen
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