[sdiy] PWM gain control

[Thomas Hudson]

I've ordered an Arduino board (http://www.arduino.cc/) to experiment  
with a microprocessor side chain controlling an all analog signal  
path for  gain manipulation (compressor, expander, guitar sustainer,  
etc).

The processor can output an analog value as a varying duty cycle PWM  
(frequency 30769 Hz). I had originally intended to use an LED/LDR to  
convert this to a resistance for controlling gain in an op amp, but  
came across an article about the Crane Song Trakker, which uses PWM/ 
FETs.

Just wondering if anyone had experience with either approach (or any  
others)? Also any suggestions on selection of FETs for this application.

Thomas