uency modulation:
</p>


<!-- LATEX
fmeq3:
\cos \, (\omega_{c}t + \!\int_{0}^{t}\! f(t) \, \mathrm{d} t)
-->

<img class="indented" src="pix/fmeq3.png" alt="cos + integral">


<p>In PM we change the phase, in FM we change the phase increment, and
to go from FM to PM, integrate the FM modulating signal.
But you can't tell which is in use 
from the output waveform; you have to know 
what the modulating signal is.  In sound synthesis, where we can do what we want with the modulating signal,
there is no essenti