[sdiy] Simple compressor, agc, ?

[Toby Paddock]

> At 12:10 PM +0000 2004/09/30, Toby Paddock wrote:
> >Howdy,
> >I'd like to build a very simple AGC type thing
> >for a "tuning display". Room mic (or whatever
> >tuning standard) gets compressed like 100% and
> >drives the horizontal of an o-scope. Whatever
> >you're playing gets compressed some and drives
> >the vertical. Then look for lissigu...
> >lissajue... lissijou...   some of those patterns.
> >
> >Need:
> >Pretty high compression.
> >Cheap and easy.
> >A few volts output. Either +/- or 0-V.
> >
> >Don't care too much about:
> >Distortion, noise, speed, freq response.
> >
> >Thanks,
> >Toby Paddock

Scott Juskiw wrote: 
> Many years ago I built the one from Craig Anderton's Electronic 
> Porkchops for Musicians book and it worked great (I still have two of 
> them). Very simple design, only 3 op amps, uses a vactrol in the 
> feedback loop. Project #8 in the book.
> 

Thanks Scott. I was thinking led with a threshold, shining 
on photo-resistor, reducing gain. But I didn't know 
exactly what to do with the resistor. That's just what 
I was looking for.   --Toby