hmmm....

> regarding FM spectrum (# of sidebands)
> p229 Curtis Roads Computer Music Tutorial pub MIT.
>
> index of modulation I is defined as
>
> I=D/M
> where D is the amount of frequency deviation (in Hz).
> if D is 100 Hz and Modulator M is 100 Hz, then the index of modulation is 1.0.
>
> fine, I is determined by two frequency values.
>

that's actually the "carrier to modulator ratio", not "Index of
Modulation" , which *is* a amplitude multiplier.
Fun thing is, you can crank that Index puppy up & down all you want,
and it will not affect the amplitude of the output (modulated carrier)
waveform. It just "spreads out" or "re-distributes" the carrier waves
energy in a pattern determined by the carrier to mod ratio, the index of
mod,
the sample rate , the original waveforms, and the math functions known
as "bessel functions" . A very good intro for musicians to these
concepts, (although one that had many typos) was the John Chowning
(father of audio FM synth) book printed by Yamaha...also out of print, I
bet...sheesh, these days I feel so old...
CharlieB

--
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Charlie Baker              baker@charlieb.com
 "when everything isn't roses, you don't get
   any headroom" - Thomas Dolby "New Toy"
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