Subject: Re: Frequency response was Re: [linux-audio-user] Audiophile CD's
From: John Lazzaro (lazzaro_AT_CS.Berkeley.EDU)
Date: Tue Jan 29 2002 - 04:10:30 EET
> Jörn Nettingsmeier writes
>
> since you have little resonators in your ear that pretty much tune
> in to one particular frequency, it really *is* picking it apart. not
> in the sense of an fft, but in the sense of thousands of tuned
> pitchforks resonating, and then "measuring" their amplitudes.
Quite true, if you're a turtle :-). Amphibian hearing systems basically
work this way, the hair cell receptors act as simple tuned resonators.
Mammals do it differently, though -- the resonance isn't a "pitch-fork"
style resonance, but instead its a specialized sort of tuning that
falls out of a complex electro-mechanical system, the cochlea. The
distinction matters, because the amount of actual resonance in the
filters are a strong function of amplitude -- at normal speaking
levels, the filter shapes are so wide they are closer to lopass filters
than band-pass filters. There's inherent non-linearity in the process
too. And, perhaps most importantly, we really don't understand how the
whole system really works yet, after 40 years of research and a dozen
generations of Ph.D. students ...
The web is full of good cochlear intro pages, at all level of abstraction,
here's a good short one to get started:
http://earlab.bu.edu/physiology/mechanics.html
--jl
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John Lazzaro -- Research Specialist -- CS Division -- EECS -- UC Berkeley
lazzaro [at] cs [dot] berkeley [dot] edu www.cs.berkeley.edu/~lazzaro
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