Vca behavior

I usually put an adsr inside the vca to drive its level. Today instead of an adsr, I used an audio signal, and to my surprise I could hear that signal in the output. I didnt think that was possible and I dont understand why. I thought whatever was inside the vca was only able to control its level.

Is that expected?

Yes. You just discovered AM (amplitude modulation).

Or to be more specific, ring modulation because you are using a bipolar VCA.

If you are interested you should definitely try some simple audio-rate signals like a sine and familiarize yourself with effect.


Ahhh I see — that makes sense now. The 301 has me learning all kinds of things. Thanks for the explanation @odevices, i’ll definitely be trying some new things!

I suppose then to use the drum sound to modulate the vca level, not at audio rate, I would have to smooth out the amplitude.

Try sending your drum signal into an envelope follower unit, then into the VCA. Guessing that might give you the effect you were originally going for.

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Thanks @Joe, thats how I originally started, but then I got very side tracked after noticing the AM effect! I’ll give it another go!