test_dynamicsCompressorNodeWithGain.html

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<head>

<meta charset="utf-8">

  <title>Test DynamicsCompressor with Gain</title>

  <script src="/tests/SimpleTest/SimpleTest.js"></script>

  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />

</head>

<body>

<script class="testbody" type="text/javascript">

SimpleTest.waitForExplicitFinish();

addLoadEvent(function() {

  var samplerate = 44100;

  var context = new OfflineAudioContext(1, samplerate/100, samplerate);

  var osc = context.createOscillator();

  osc.frequency.value = 2400;

  var gain = context.createGain();

  gain.gain.value = 1.5;

  // These numbers are borrowed from the example code on MDN

  // https://developer.mozilla.org/en-US/docs/Web/API/DynamicsCompressorNode

  var compressor = context.createDynamicsCompressor();

  compressor.threshold.value = -50;

  compressor.knee.value = 40;

  compressor.ratio.value = 12;

  compressor.reduction.value = -20;

  compressor.attack.value = 0;

  compressor.release.value = 0.25;

  osc.connect(gain);

  gain.connect(compressor);

  compressor.connect(context.destination);

  osc.start();

  context.startRendering().then(buffer => {

    var peak = Math.max(...buffer.getChannelData(0));

    console.log(peak);

    // These values are experimentally determined. Without dynamics compression

    // the peak should be just under 1.5. We also check for a minimum value

    // to make sure we are not getting all zeros.

    ok(peak >= 0.2 && peak < 1.0, "Peak value should be greater than 0.25 and less than 1.0");

    SimpleTest.finish();

});

});

</script>

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