Thank you very much chysn, the LFO analogy is very helpful. I don't have a Prophet yet, but I am very curious, and often I get lost on tangents, searching the web. (Found a great & historically interesting discussion on this in KVR, 2005.)
It reminds me of the FM concept. Osc 1 modulating the filter, analogous to a modulator oscillator modulating a carrier oscillator. Except, filter alone, not self-oscillating, is like a silent ghost?
I'm trying to wrap my head around:
A filter applied to a sounding Osc 1, whose waveshape is concurrently modulating said filter. Like oscillator feedback, one step removed?
I wonder about ...
1. I have read the filter can self-oscillate at audio rates. If you apply Osc 1 (sans volume, osc 2 shape off) to the self resonating filter, is this primitive FM?
2. Can audible self-oscillating filter be at a low pitch, like C3? (as opposed to only high zones, like C6.) I'd assume yes.