about 200 pages. was published in japan by yamaha, who obviously... wrote the book on Frequency Modulation. there are a lot of logarithmic graphic representations, from start to end, but FM is a super complex mathematical function that literally does not stop, what is flying through the air to your ears is computed to interact, respond, morph, and finally arrive in a certain precomputed fashion.
at it's simplest, as i would explain it, and i've been trapped in ... dealing with FM for a very long time, is that each pair of carrier sounds will have it's properties, modulated at a specific pitch, and the waves react to each other, cancelling or enhancing certain aspects. if you have two sine waves, for instance, 180 degrees out of phase, you end up in a negative phase, so the synth engine tries to compensate for all of this in doing incredibly complex modifications to the MODULATIONS of the FREQUENCIES on the fly. it's how DSP used to get done...
it is all in reerence to the INfamous yamaha DX7, a super early and super crappy implementation.
This is the best resource I have ever found on the subject of FM synthesis. It is written in a straight-forward and encouraging tone that never, ever feels condescending or tendious.
(And it helps that one of the writers is one of the inventors of the technologies and techniques being discussed.)
Clearly written and thoughtfully illustrated introduction for anyone musically inclined and curious about the inner workings of FM synthesis. Suitable for less-math-oriented readers, with appendices for getting a little deeper into the details.