Mercurial > hg > js-dsp-test

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <script src="../lib/complex_array.js"></script>
  <script src="../lib/fft.js"></script>
  <link rel="stylesheet" href="example.css">
  <title></title>
</head>
<body>
  <div class="panel">
    <div id="original" class="example"></div>
    <div class="explanation">
      Sample data
      <pre>
var data = new ComplexArray(128)
data.map(function(value, i, n) {
  value.real = (i > n/3 &amp;&amp; i &lt; 2*n/3) ? 1 : 0
})
      </pre>
    </div>
  </div>
  <div class="panel">
    <div id="fft" class="example"></div>
    <div class="explanation">
      Transform (in place):<br>
      <code>
        data.FFT()
      </code>
    </div>
  </div>
  <div  class="panel">
    <div id="fft_filtered" class="example"></div>
    <div class="explanation">
      Simple low pass filter:
      <pre>
data.map(function(freq, i, n) {
  if (i > n/5 &amp;&amp; i &lt; 4*n/5) {
    freq.real = 0
    freq.imag = 0
  }
})
      </pre>
    </div>
  </div>
  <div class="panel">
    <div id="original_filtered" class="example"></div>
    <div class="explanation">
      Transform back:<br>
      <code>
        data.InvFFT()
      </code>
    </div>
  </div>
  <div class="panel">
    <div id="all_in_one" class="example"></div>
    <div class="explanation">
      ... or all in one step
      <pre>
data.frequencyMap(function(freq, i, n) {
  if (i > n/5 &amp;&amp; i &lt; 4*n/5) {
    freq.real = 0
    freq.imag = 0
  }
})
      </pre>
    </div>
  </div>
  <script>
    !function() {
      function drawToCanvas(element_id, data) {
        var
          element = document.getElementById(element_id)
          canvas = document.createElement('canvas'),
          context = canvas.getContext('2d'),
          width = element.clientWidth,
          height = element.clientHeight,
          n = data.length

        canvas.width = width
        canvas.height = height
        element.appendChild(canvas)

        context.strokeStyle = 'blue'
        context.beginPath()
        data.forEach(function(c_value, i) {
          context.lineTo(
            i * width / n,
            height/2 * (1.5 - c_value.real)
          )
        })
        context.stroke()
      }

      window.onload = function() {
        var
          data = new complex_array.ComplexArray(128)

        data.map(function(value, i, n) {
          value.real = (i > n/3 && i < 2*n/3) ? 1 : 0
        })

        drawToCanvas('original', data)

        data.FFT()
        drawToCanvas('fft', data)
        data.map(function(freq, i, n) {
          if (i > n/5 && i < 4*n/5) {
            freq.real = 0
            freq.imag = 0
          }
        })
        drawToCanvas('fft_filtered', data)
        drawToCanvas('original_filtered', data.InvFFT())

        drawToCanvas('all_in_one', data.frequencyMap(function(freq, i, n) {
          if (i > n/5 && i < 4*n/5) {
            freq.real = 0
            freq.imag = 0
          }
        }))
      }
    }()
  </script>
</body>
</html>
author	Chris Cannam
date	Tue, 10 Nov 2015 07:30:50 +0000
parents	66f9fd5ac611
children