eived as a frequency change).  We 
can express this (the vibrato, not the neat story) as:
</p>

<!-- LATEX \[\cos \, (\omega_{c}t+f(t))\] -->

<img class="indented" src="pix/fmeq1.png" alt="cos(wt + f)">

<p>where the c subscript stands for "carrier" and f(t) means "some arbitrary function added to the 
carrier".  Since cos takes an angle as its argument, f(t) modulates (that is, changes) the angle 
passed to the cosine, hence the generic name "angle modulation".  We can add that change either to
the argume