[sdiy] FM math question

[ASSI]

On Mittwoch 15 Oktober 2008, Magnus Danielson wrote:
> As you waveshape to sine it is very simple and infact maps very
> neatly into the theory.

I don't think he does what you describe.  From the electro-music 
thread the signal path appears to be an (analog) sawtooth core into a 
fullwave rectifier into an OTA sine shaper.  Unless I'm missing 
something, there is no phase-to-sine mapping anywhere in this signal 
path, but there are two nonlinearities.  The question posed by Ian 
(again if I understand it correctly) now is why the resulting signal 
has approximately the same spectrum as doing a PM on a sinewave.

> This is expected.

Tell me how. :-)  A somewhat unscientific argument would be that both 
nonlinearities produce spectra with fast decaying tails, so you could 
explain why the higher order modulation products don't end up 
counting much in the grander scheme of things.



Achim.
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