Filter Frequency Modulation

[Daniel Gendreau]

> I'm building a few of Tomg's filters and I'm wondering if I can add FM
> modulation from an audio signal to replace a CV input.  Also would it be
> possible to do one big audio to CV converter that I could build one of
> and use to modulate anything I wanted to.
> Rob Rickner

Method #1: (sounds similar to ring modulation)
As far as I know, you can feed audio right into the CV jack. You may want to
adjust the gain of the audio with a pot first. This is the easier of the
two.

Method #2: (aka. Auto Wah)
Another andio control method extracts the volume envelope from the audio.
This usually involves rectifying(full or 1/2 wave) the audio signal and
using a diode/capacitor to give a 0 attack / fixed(controlled by a pot)
decay rate. It is very similar to an AC voltage regulator from a power
supply. From there, you low pass filter the envelope (to take out the
jaggies) and probably do an expo conversion.

Hope that helps,
-Dan G.