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DIY Stompboxes => Digital & DSP => Topic started by: cloudscapes on November 02, 2014, 07:46:55 PM

Title: Resonator brainstorming..
Post by: cloudscapes on November 02, 2014, 07:46:55 PM
Hey all,

I thought it would be fun to start a thread where we can brainstorm DIY resonators. Seeing as how it's an effect we don't see very often in hardware. The reference I'm gonna use here is Ableton's resonator:

http://www.youtube.com/watch?v=jtciKmwVoTE
(sorry for the club music, posted mainly for the explanation)

Another, more to my liking:
http://www.youtube.com/watch?v=Tf83Lysb8zE

(http://macprovid.vo.llnwd.net/o43/hub/media/1099/7709/02_-_Resonators.png)

At it's simplest, the idea is that you can tune half a dozen notes (via knobs), and if the instrument harmonics approach the pitch of any of the tuned pitches, you get a resonation. With decay time, as a bonus. I can think of two ways to possibly do this:

1. On a PIC/ARM/DSP, free fourier transform the input to get a good idea of your main harmonics. If you get a lot on one of a few tuned frequencies, you either use a digital oscillator to be mixed with the analog signal, or you could have the micro drive a DCO. I've never done FFT mind-you, and I suck at math, so I may be horribly wrong with this.

2. An analog way, have as many resonant filters as you want resonators. Crank the resonance, somehow grab onto just the resonation feedback, and use that as the oscillator to be mixed with the signal. Filter cutoff controls resonating frequency, of course.
Title: Re: Resonator brainstorming..
Post by: Digital Larry on November 03, 2014, 08:50:29 AM
How about:

1) 2-pole state variable filter with high resonance settings.  Very very close to any analog implementation but much easier to control and reproduce as there are no "component tolerances" to deal with.

2) Short delay lines/all-pass filters again with high feedback settings.  Have to watch the input gain as feedback increases.
Title: Re: Resonator brainstorming..
Post by: ElectricDruid on November 27, 2014, 04:38:42 PM
How about:

1) 2-pole state variable filter with high resonance settings.  Very very close to any analog implementation but much easier to control and reproduce as there are no "component tolerances" to deal with.

2) Short delay lines/all-pass filters again with high feedback settings.  Have to watch the input gain as feedback increases.

Another vote for a digital filter approach. Going via an FFT sounds like too much work. There's lots of stuff about various filters that might be suitable, and the SVF or allpass are good ideas.

Tom