third_party/web_platform_tests/webaudio/the-audio-api/the-gainnode-interface/test-gainnode.html

<!doctype html>

<!--
Tests that GainNode is properly scaling the gain.
We'll render 11 notes, starting at a gain of 1.0, decreasing in gain by 0.1.
The 11th note will be of gain 0.0, so it should be silent (at the end in the rendered output).

Based on a test from the WebKit test suite
(https://github.com/WebKit/webkit/blob/master/LayoutTests/webaudio/gain.html)
-->

<html class="a">
 <head>
  <title>GainNode interface</title>
  <script src="/resources/testharness.js"></script>
  <script src="/resources/testharnessreport.js"></script>
  <script src="/webaudio/js/lodash.js"></script>
  <script src="/webaudio/js/vendor-prefixes.js"></script>
  <script src="/webaudio/js/helpers.js"></script>
  <script src="/webaudio/js/buffer-loader.js"></script>
 </head>
 <body class="a">
  <div id="log"></div>
  <script>
var gainNodeTest = async_test("GainNode");

var sampleRate = 44100.0;
var bufferDurationSeconds = 0.125;
var numberOfNotes = 11;
var noteSpacing = bufferDurationSeconds + 0.020; // leave 20ms of silence between each "note"
var lengthInSeconds = numberOfNotes * noteSpacing;

var context = 0;
var expectedBuffer = 0;
var actualBuffer = 0;
var sinWaveBuffer = 0;

function createSinWaveBuffer(lengthInSeconds, frequency) {
  var audioBuffer = context.createBuffer(2, lengthInSeconds * sampleRate, sampleRate);

  var n = audioBuffer.length;
  var channelL = audioBuffer.getChannelData(0);
  var channelR = audioBuffer.getChannelData(1);

  for (var i = 0; i < n; ++i) {
    channelL[i] = Math.sin(frequency * 2.0*Math.PI * i / sampleRate);
    channelR[i] = channelL[i];
  }

  return audioBuffer;
}

function playNote(time, gain) {
  var source = context.createBufferSource();
  source.buffer = sinWaveBuffer;

  var gainNode = context.createGain();
  gainNode.gain.value = gain;

  source.connect(gainNode);
  gainNode.connect(context.destination);

  source.start(time);
}

function loadExpectedBuffer(event) {
  actualBuffer = event.renderedBuffer;

  bufferLoader = new BufferLoader(
    context,
    ['/webaudio/the-audio-api/the-gainnode-interface/gain-expected.wav'],
    bufferLoadCompleted
  );
  bufferLoader.load();
};

function bufferLoadCompleted(buffer) {
  compareExpectedWithActualBuffer(buffer);
};

setup( function() {
  // Create offline audio context.
  context = new OfflineAudioContext(2, sampleRate * lengthInSeconds, sampleRate);

  // Create a buffer for a short "note".
  sinWaveBuffer = createSinWaveBuffer(bufferDurationSeconds, 880.0);

  // Render 11 notes, starting at a gain of 1.0, decreasing in gain by 0.1.
  // The last note will be of gain 0.0, so shouldn't be perceptible in the rendered output.
  for (var i = 0; i < numberOfNotes; ++i) {
    var time = i * noteSpacing;
    var gain = 1.0 - i / (numberOfNotes - 1);
    playNote(time, gain);
  }

  context.oncomplete = loadExpectedBuffer;
  context.startRendering();
}, {timeout: 10000});

function compareExpectedWithActualBuffer(expected) {
  var expectedBuffer = expected[0];

  gainNodeTest.step(function() {
    assert_array_approx_equals(expectedBuffer.getChannelData(0),
                               actualBuffer.getChannelData(0),
                               1e-4,
                               "comparing expected and rendered buffers (channel 0)");
  });

  gainNodeTest.step(function() {
    assert_array_approx_equals(expectedBuffer.getChannelData(1),
                               actualBuffer.getChannelData(1),
                               1e-4,
                               "comparing expected and rendered buffers (channel 1)");
  });

  gainNodeTest.done();
};
  </script>
 </body>
</html>