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From: raoul@eplunix.UUCP (Nico Garcia)
Newsgroups: comp.dsp
Subject: Re: AGC with DSP...
Message-ID: <1078@eplunix.UUCP>
Date: 9 May 91 17:27:15 GMT
References: <15511@darkstar.ucsc.edu> <1991May9.043958.23925@netcom.COM>
Organization: Eaton-Peabody Lab, Boston, MA
Lines: 27

In article <1991May9.043958.23925@netcom.COM>, mcmahan@netcom.COM (Dave Mc Mahan) writes:
>  In a previous article, sutin@helios (Brian Sutin) writes:
> >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.

Hmmm. After analyzing some AGC's in circuits, I've picked up a personal
distaste for them. They tend to do some very strange things to your harmonic
distortion as well. However, one way to do it is to peak sample your signal,
(both +/- peaks, actual circuit left as an exercise to the reader),
digitally read that (since who knows, you may want the information for
something) and use it to set an AD7111 programmable logarithmic attenuator.
Analog Devices makes them, and they're kind of nice.

To avoid AGC's all together, use several A/D's with overlap in their signal
ranges, generate a lookup table for input vs. output readings, and send
*that* to your computer. Do your AGC in software this way, where it won't
inject weirdness into your signal analysis.

Is this for speech or some other audio function?

-- 
			Nico Garcia
			Designs by Geniuses for use by Idiots
			eplunix!cirl!raoul@eddie.mit.edu