ignal: 
FM(white-noise) = PM(brownian-noise).  Similarly,
FM(square-wave) = PM(triangle-wave), 
FM(nxy1sin) = PM(square-wave), and
FM(e^x) = PM(e^x).  FM(square-wave) is:
</p>

<img class="indented" src="pix/fmeq58.png" alt="fm(noise)">.

<!-- LATEX fmeq58:  (Klapper p102)
  &\sum_{n=-\infty}^{\infty} \frac{2B}{\pi(B^{2}-n^{2})} \sin(\frac{\pi}{2} (B-n)) \sin (\omega_{c}+n\omega_{m})t
-->


<!--
;; FM(sq)=PM(tri):
(define* (fmpmsq beg dur freq amp (mc-ratio 1) (index 1.0) (phase (* 0.5 pi)))
  (let* ((start