{i}(B_{1})J_{k}(B_{2})\sin(\omega_{c} + i\omega_{m1} + k\omega_{m2})t \\
-->
<img class="indented" src="pix/fmeq32.png" alt="2 sums">

<p>You can chew up any amount of free time calculating the resulting side band amplitudes &mdash; see the immortal classic:
Schottstaedt, "The Simulation of Natural Instrument Tones Using Frequency Modulation with a 
Complex Modulating Wave".  (There's a function to do it for you in dsp.scm: fm-parallel-component). 
In simple cases, the extra modulating components flatten an