; here is the fm integration
       (setf val (* amp (sin carrier-phase)))
       (incf carrier-phase carrier-phase-incr)
       (incf modulator-phase modulator-phase-incr)
       (outa i val)))))

(with-sound () (pm 0 10000 1000 .5 0.25 4))
(with-sound () (fm 0 10000 1000 .5 0.25 4))
</pre>
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<!-- SND CASE -->
<pre class="indented">
(define (pm beg end freq amp mc-ratio index)  ; "mc-ratio" = modulator to carrier frequency ratio
  (let ((carrier-phase 0.0) ; set to pi/2 if someone tells you PM can't pro