Electret capsules seem like a low power and cheap way to generate CV. I was wondering if anyone had experience using them

The "problem" with them when used for audio is that you have to use a capacitor to block DC. :) It seems like you could use them almost in the opposite way as an envelope follower, that is, with bi-polar control.

I don't have a scope though, so I'm not sure exactly what's happening when I experiment with them! :)

http://en.wikipedia.org/wiki/Electret_microphone
http://www.epanorama.net/circuits/microphone_powering.html