Re: Noise source processing
-----Original Message----- From: mgraffam@mhv.net <mgraffam@mhv.net> Date: Thursday, August 06, 1998 10:17 AM [[...]>The noise coming off of the sound card is more beige than white though..
Does anyone know of any papers, articles or whatever on good techniques to remove bias from the audio source?
My initial thoughts are along the lines of just hashing everything, but this will be slow, and I'd like to see what other ideas are out there.
What about an analog filter placed before the digitizer? Nowadays there should be inexpensive single-chip implementations of multiple-tap equalizers made for consumer audio. You just have to straighten up the amplitude ignoring the phase rotation, because the power spectrum is a real-codomain function (being the Fourier Transform of the autocorrelation, which is an even function). It won't be perfect, but it'll help. Enzo
At 11:34 PM 8/6/98 +0800, Enzo Michelangeli wrote:
[[...]>The noise coming off of the sound card is more beige than white though..
Does anyone know of any papers, articles or whatever on good techniques to remove bias from the audio source?
My initial thoughts are along the lines of just hashing everything, but this will be slow, and I'd like to see what other ideas are out there.
What about an analog filter placed before the digitizer?
The engineering issue is this: no matter how great you filter out the junk, you don't have a perfect analog measurement to start with. (Note that filtering out junk reduces info content). So the question is how to distill the bits out of your binary digits. You need to reduce the number of bits; you need to make them equiprobable. I have not had luck*time implementing Shannon's method for distilling bits, mentioned as suggestion #2 in the RFC. This method produces perfect 0:1 ratio but takes indeterminate input bits to do so. Please post if you play with this. honig@alum.mit.edu
participants (2)
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David Honig -
Enzo Michelangeli