Feedback Effect (Freqout, AcouFiend, etc)

[recursinging]

@donstavely

I lead myself down the rabbit hole of pitch detection - positive and negative peak detection, the peaking filter bank, even a sparse autocorrelation idea I wanted to try. None of them were really robust on real-world guitar clips I used as test cases.

This. I’ve also been down in this rabbit hole for the better part of a year now. Time domain pitch detection is a hard problem, and often ideas that work really well on synthesized waveforms fall flat on real world audio.

Joel’s BACF implementation from the Q library is by far the most robust I’ve found, and it is efficient enough for a the 50 to 500Hz I’m looking to cover with the Daisy Seed. But the implementation is complicated because it contains solutions to the problems real world signals present - hysteresis for noise, bias for stability, etc.

@donstavely

A guitarist standing in front of his amp is, at its simplest, a delay of around a millisecond per foot of separation. Beyond that, there are the characteristics of the amp and speaker. So we could add an amp and cabinet sim in series with a delay? Beyond that, how does the sound from the speaker interact with the strings? It is probably a complex process, but maybe trying to model it is overkill.

I agree, the most relevant part of this system, in terms of achieving this effect, is the relationship between the vibration caused by the speaker, and the high Q filter that is an electric guitar string. While this system can probably be whittled down to a feedback loop and a few filters, the “finger position on fret board” parameter is tricky part.

@donstavely

I bring it up in all humility, realizing that Boss did in 1985 with op amps and CMOS logic what I can’t do as well today with a Cortex M7!

What you can’t do as well with a Cortex M7 yet. Your constraint here is knowledge. The engineers at Boss in 1985 had an entirely different set of constraints (and resources!).