VCA does things(almost) on its own?

So, when I was testing out some VCA, I discovered something rather odd. To me that is. I made some connections which I then disconnected from the VCO and a filter and guess what? The CVA with an lfo connected to its lower input, kept giving audio on its own! When I reconstructed this part of the patch, nothing would sound. Not unless I gave the VCA some kind of input. Also when I closed the file/patch and then loaded it again, the VCA would need some kind of feed in, an infusion if you like, to produce audio. Now this might be an uber-noob question, but what am I missing here? Does the lfo do the trick? Anyway, it makes some nice drum kick sound anyway! See the patch picture.

Hi @Stanley

This is because this VCA has feedback.

Very generally put, I would describe feedback as influencing the output of something with the output itself. Most of the time that’s just adding a bit of the output of an effect to its input.

You probably know feedback from delay effects, where it is used to get multiple echos, but it is used in all kinds of modules. E.g: feeding back the output of some kind of distortion to its input sounds pretty cool most of the time. That’s exactly what the VCA in your patch does. That VCA (aside from attenuating a signal) also has a distortion effect built into it that has a feedback control.

image
(this knob)

When you feed back enough of the signal, you get an infinite feedback loop, where the signal isn‘t getting quieter during feedback and therefor infinitely feeds back.

This obviously needs an initial input that can be fed back.

So whats happening in your patch is that you have the VCAs feedback and distortion turned up enough to create an infinite feedback loop. When you open up the patch there is nothing that can be fed back, but as soon as you put something into the VCA it will feedback for ever, resulting in a constant output of the VCA.

Just a quick warning though before you go on and experiment with feedback loops yourself:
Feedback can be pretty dangerous.
If you don’t have anythig, that restricts the feedback in any way and you feed back 100% or more, the signal can build up to incredibly loud sounds which can potentially damage your speakers and your ears.

The standard audio signal in Audulus is between -1 and 1 but a signal can go up much MUCH higher and Audulus doesn’t stop you from sending out ridiculously loud signal through the speaker node.
(The VCA has restricted feedback, because the distortion clips off everything that goes above standard audio level)

Thank you so much for the explanation! It really makes sense now. Helped also with other stuff I’m experimenting with. I have a limiter set to the output. I once experienced an exponential feedback years ago. That was one time enough! Thanks again!

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