Message-Id: <m10B0GE-000S5eC@inti.gov.ar>
Comments: Authenticated sender is <salvador AT natacha DOT inti DOT gov DOT ar>
From: "Salvador Eduardo Tropea (SET)" <salvador AT inti DOT gov DOT ar>
Organization: INTI
To: Shawn Hargreaves <ShawnH AT Probe DOT co DOT uk>, djgpp AT delorie DOT com
Date: Thu, 11 Feb 1999 14:53:50 +0000
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Subject: Re: sound spectrum analysis
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Reply-To: djgpp AT delorie DOT com

Shawn Hargreaves <ShawnH AT Probe DOT co DOT uk> wrote:

> Cminnican writes:
> > I am interested in writing some code to analyse sound in realtime 
> > through the line in input on my soundcard. I would like to be able 
> > to extract certain frequencies from the incoming sound and use these 
> > values to create visual effects that respond to the music as it is 
> > playing. 
> 
> You need to do a Fourier analysis of the input data. That's quite a
> complex operation, but you can probably find some code for it on the
> net (sorry, I don't know where). Alternatively, you should be able
> to find descriptions of the algorithm in a computing or math textbook:
> check the library.

Some recomendations about the topic:

1) Use an integer math version of the FFT algorithm. It works even in 486 PCs 
and you can update the screen at 70 fps.
2) Apply some windowing algorithm to the data or you'll calculate the 
spectrum of the rect and the data (convolutioned).
3) Look in some DSP or Signal processing book to find the algorithm. Some 
years ago I adapted one for the Intel 8096 family of processors to C + i386 
code, the algorithm was *very* fast.

SET
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