[sdiy] Additive Synthesis questions

Aaron Lanterman lanterma at ece.gatech.edu
Fri Jun 11 07:36:53 CEST 2010

On Jun 1, 2010, at 4:40 AM, Stewart Pye wrote:

>> The basic idea is that he puts one of those diode bridges (like you see in the Yamaha GX-1 aka the MOTM-485, or the Korg-50 VCF and VCA) in the *feedback loop* of an op amp.

> That sounds like it could be a deadband circuit.

It is one. :)

> I can see how you could get doubling of frequency of a triangle wave if you mixed the output of the deadband circuit with the input. You could get variation in the waveshape by varying the input level but if you set it at a certain point you'd get a frequency doubled triangle wave. I could be way off here...
> What I can't understand is how serge or Buchla got *3, *5 etc frequency. Could anyone shed some light on this?

Add up the outputs of a bunch of deadband circuits, each with increasingly wide deadbands, but with alternating sines; you'll get a nonlinearity with a bunch of triangular-shaped "teeth." Then puzzle out what happens to triangle waves that are passed through that as the amplitude varies and it hits more and more "teeth."

- Aaron

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