[sdiy] Looking for help with Bessel functions and FM

[Glen]

I have a pet project that I'd like to get started on. I would like to
analyze an FM synthesizer patch and calculate the theoretical output
spectrum that would exist any given moment when playing one note using that
patch. What I would like to eventually do with that ability is translate an
FM synth patch into an additive synth patch.

I think Bessel functions are something I need to learn about for this
project, but I'm having trouble finding enough information, especially in a
format that I can understand. Does anyone know of any good FM modulation
and/or Bessel function tutorials?

thanks,
Glen