ne wave.
</p>

<pre class="indented">
(define (feedbk beg dur freq amp index)
  (let* ((start (seconds-&gt;samples beg))
	 (end (+ start (seconds-&gt;samples dur)))
	 (y 0.0)
	 (x-incr (hz-&gt;radians freq)))
    (do ((i start (+ i 1))
         (x 0.0 (+ x x-incr)))
        ((= i end))
      (set! y (+ x (* index (sin y))))
      (outa i (* amp (sin y))))))

(with-sound () (feedbk 0 1 100.0 1.0 1.0))
</pre>

<table class="borderedm">
<tr><td>
<img src="pix/fdbk.png" alt="feedback fm">
</td></tr>
<tr>
<td>
<