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From: sutin@helios (Brian Sutin)
Newsgroups: comp.dsp,sci.electronics
Subject: AGC with DSP...
Message-ID: <15511@darkstar.ucsc.edu>
Date: 8 May 91 00:41:20 GMT
Sender: usenet@darkstar.ucsc.edu
Reply-To: sutin@helios (Brian Sutin)
Followup-To: comp.dsp
Organization: Lick Observatory UCSC
Lines: 29



I am using a 12-bit DSP system to do real time processing on full frequency
range audio signals.  Because of the dynamic range in volume, however, 12 bits
is very inadequate at low signal levels.  The solution for my application,
since I do not need to know the actual volume, is to use an analog circuit
similar to an AGC:

     INPUT--->AMP 1--->DSP--->AMP 2--->OUTPUT
       |        ^               ^
       v        |               |
     POWER-----------------------

Here POWER calculates the power of the input signal, which is filtered at
something like 10Hz.  AMP 1 takes the input signal and amplifies/de-amplifies
the output to be about 1v.  AMP 2 takes the output from the DSP, also about
1v, and amplifies/de-amplifies back to the original volume level.  If both
amplifiers are linear to 12 bits over the entire power and frequency range,
then the entire configuration should have no audible distortion.

Since my circuit design knowledge is not up to this level, I have no idea
how to actually implement this application.  I cannot believe that someone
out there hasn't already done this, or doesn't have something better.

Any input by e-mail appreciated.

Brian Sutin
Lick Observatory, UCSC
sutin@helios.ucsc.edu