[Nyquist-users] Where did the algorithm in fmosc.alg come from? (Pitch instabilities?)

[Wesley T. M. <wes...@ju...>]

I'm having a problem keeping pitch stable with fmosc, and was wondering where the algorithm came from. Here are some SAL code examples.

When I do something like this:

set env = pwl(2.0, 500.0, 2.001)
set mod1 = osc(c3, 2.0) * env
set carrier = fmosc(c3, mod1)
play carrier

...the resulting pitch is stable. However, if I add another layer of modulation:

set env = pwl(2.0, 500.0, 2.001)
set mod1 = osc(c3, 2.0) * env
set mod2 = fmosc(c3, mod1) * env
set carrier = fmosc(c3, mod2)
play carrier

...the pitch sweeps all over the place. (Actually, there is no clearly perceived pitch.)

I'm 99.9% sure DX7's and other Yamaha FM synths don't do this for stacked modulators. I suppose I could pull out my DX7-II and double check.

Wes Morrison

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