Help/UGens/FFT/SpecPcile.html

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  27 <p class="p1"><b>SpecPcile<span class="Apple-tab-span"> </span>Find a percentile of FFT magnitude spectrum</b></p>
  28 <p class="p2"><br></p>
  29 <p class="p3"><b><span class="Apple-tab-span">  </span>SpecPcile.kr(chain, fraction)</b></p>
  30 <p class="p4"><br></p>
  31 <p class="p3">Given an <a href="FFT.html"><span class="s1">FFT</span></a> chain this calculates the cumulative distribution of the frequency spectrum, and outputs the frequency value which corresponds to the desired percentile.</p>
  32 <p class="p4"><br></p>
  33 <p class="p3">For example, to find the frequency at which 90% of the spectral energy lies below that frequency, you want the 90-percentile, which means the value of <i>fraction</i> should be 0.9. The 90-percentile or 95-percentile is often used as a measure of <b><i>spectral roll-off</i></b>.</p>
  34 <p class="p4"><br></p>
  35 <p class="p3">The optional third argument <b>interpolate</b> specifies whether interpolation should be used to try and make the percentile frequency estimate more accurate, at the cost of a little higher CPU usage. Set it to 1 to enable this.</p>
  36 <p class="p4"><br></p>
  37 <p class="p4"><br></p>
  38 <p class="p3"><b>Examples:</b></p>
  39 <p class="p2"><br></p>
  40 <p class="p5">s = <span class="s2">Server</span>.internal.boot;<span class="Apple-converted-space"> </span></p>
  41 <p class="p5">b = <span class="s2">Buffer</span>.alloc(s,2048,1);</p>
  42 <p class="p6"><br></p>
  43 <p class="p7">// Simple demo with filtering white noise, and trying to infer the cutoff freq.</p>
  44 <p class="p7">// Move the mouse.</p>
  45 <p class="p5">(</p>
  46 <p class="p5">{</p>
  47 <p class="p5"><span class="s2">var</span> in, chain, realcutoff, estcutoff;</p>
  48 <p class="p5">realcutoff = <span class="s2">MouseX</span>.kr(0.00001,22050);</p>
  49 <p class="p5">in = <span class="s2">LPF</span>.ar(<span class="s2">WhiteNoise</span>.ar, realcutoff);</p>
  50 <p class="p5">chain = <span class="s2">FFT</span>(b, in);</p>
  51 <p class="p5">estcutoff = <span class="s2">Lag</span>.kr(<span class="s2">SpecPcile</span>.kr(chain, 0.9), 1);</p>
  52 <p class="p5">realcutoff.poll(<span class="s2">Impulse</span>.kr(1), <span class="s3">"real cutoff"</span>);</p>
  53 <p class="p5">estcutoff.poll(<span class="s2">Impulse</span>.kr(1), <span class="s3">"estimated cutoff"</span>);</p>
  54 <p class="p5"><span class="s2">Out</span>.ar(0, in);</p>
  55 <p class="p5"><span class="s2">Out</span>.kr(0, estcutoff * 22050.0.reciprocal);</p>
  56 <p class="p5">}.scope;</p>
  57 <p class="p5">)</p>
  58 <p class="p6"><br></p>
  59 <p class="p7">// Audio input - try different vowel/long-consonant sounds and see what comes out.</p>
  60 <p class="p7">// Specifically, change from "ssss" through to "aaaa" through to "wwww".</p>
  61 <p class="p5">(</p>
  62 <p class="p5">{</p>
  63 <p class="p5"><span class="s2">var</span> in, chain, perc;</p>
  64 <p class="p5">in = <span class="s2">SoundIn</span>.ar([0,1]).mean;</p>
  65 <p class="p5">chain = <span class="s2">FFT</span>(b, in);</p>
  66 <p class="p7">//Out.ar(0, in * 0.1);</p>
  67 <p class="p8"><span class="s4">perc = </span><span class="s2">SpecPcile</span>.kr(chain, 0.5);</p>
  68 <p class="p7"><span class="s2">Out</span><span class="s5">.ar(1, </span><span class="s2">LPF</span><span class="s5">.ar(</span><span class="s2">WhiteNoise</span><span class="s5">.ar, perc)); </span>//NB Outputting to right channel - handy on PowerBooks</p>
  69 <p class="p5"><span class="s2">Out</span>.kr(0, perc * 22050.0.reciprocal);</p>
  70 <p class="p5">}.scope;</p>
  71 <p class="p5">)</p>
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