))
</pre>

<p>is clarinet-like.  Now start at 2000 Hz, set the mc-ratio to .1, and
sweep the FM index from 0 to 10, and the spectrogram looks like this:
</p>

<img src="pix/fmsweep.png" alt="sweep index">

<p>
There is a lot of music in simple FM.  You get a full spectrum at little computational expense, and
the index gives you a simple and intuitive way to change that spectrum.
Since the output peak amplitude
is not affected by the modulating signal (cos(x) is between -1 and 1 no matter what x is, as long 