(it works only with X window system at moment)
        to control the cutoff of the filter.
      </p>

      <pre class="src src-lisp">(<span style="color: #8deeee;">define-vug</span> <span style="color: #87cefa;">pv-lp-wall</span> ((abuf abuffer) threshold)
  (dofft-polar (i nbins ((compute-abuffer abuf)) () <span style="color: #b0c4de;">:result</span> abuf)
    (<span style="color: #8deeee;">if</span> (&gt;= i (sample-&gt;fixnum threshold))
        (setf mag0 0.0d0))))

(<span style="color: #8deeee;">dsp