[sdiy] (OT?) FEEDBACK as a topic in electronics, music, science, etc?? BOOKS?

[Scott Nordlund]

> Great thread and since I've been meaning to ask about this as well - I thought this question might be relevant. Hope you don't mind Dan.
>
> Can anyone comment on the main qualities affecting 'musical' (or, I guess, in the case of video - 'artistic') feedback?
>
> Is it...
>
> a) The time delay - e.g. the time it takes a signal to get from the speakers of my amp and back into my guitar pickups
> b) The change in the shape of the waveform e.g. small inaccuracies that start to stack up infinitely
> c) Other...

I think what generally makes it interesting is chaotic behavior. Rather than a stable oscillation (limit cycle), it can, for instance, transition between a number of different states at unpredictable intervals. But this is really general. It can happen on an audio timescale (producing a noisy waveform) or over minutes. And this isn't necessarily musical or non-musical by itself, it's far more dependent on how you're using it (the way it's mapped to audible parameters). To listen directly to the output may sound awful, but you can use it to modulate pitch or something else. The interesting part is that the sound essentially determines its own behavior and produces complex output without direct user intervention. The "composition" is the algorithm; the specifics take care of themselves. You can do this with complex synth patching, mixer feedback, neural networks, feedback through effect processors, self-observing and adaptive systems, etc.
Video feedback can produce more immediately interesting results. The mapping of the sensor's pixels to the monitor's pixels, the nonlinear control of brightness via AGC and the time delay from frame to frame can easily produce fractal and cellular automata type things.