third_party/WebKit/LayoutTests/webaudio/gain.html

   1 <!DOCTYPE html>
   2
   3 <!--
   4 Tests that GainNode is properly scaling the gain.
   5 We'll render 11 notes, starting at a gain of 1.0, decreasing in gain by 0.1.
   6 The 11th note will be of gain 0.0, so it should be silent (at the end in the rendered output).
   7 -->
   8
   9 <html>
  10 <head>
  11 <script type="text/javascript" src="resources/audio-testing.js"></script>
  12
  13 </head>
  14 <body>
  15
  16 <script>
  17
  18 window.onload = init;
  19
  20 var sampleRate = 44100.0;
  21 var bufferDurationSeconds = 0.125;
  22 var numberOfNotes = 11;
  23 var noteSpacing = bufferDurationSeconds + 0.020; // leave 20ms of silence between each "note"
  24 var lengthInSeconds = numberOfNotes * noteSpacing;
  25
  26 var context = 0;
  27 var sinWaveBuffer = 0;
  28
  29 function createSinWaveBuffer(lengthInSeconds, frequency) {
  30     var audioBuffer = context.createBuffer(2, lengthInSeconds * sampleRate, sampleRate);
  31
  32     var n = audioBuffer.length;
  33     var channelL = audioBuffer.getChannelData(0);
  34     var channelR = audioBuffer.getChannelData(1);
  35
  36     for (var i = 0; i < n; ++i) {
  37         channelL[i] = Math.sin(frequency * 2.0*Math.PI * i / sampleRate);
  38         channelR[i] = channelL[i];
  39     }
  40
  41     return audioBuffer;
  42 }
  43
  44 function playNote(time, gain) {
  45     var source = context.createBufferSource();
  46     source.buffer = sinWaveBuffer;
  47
  48     var gainNode = context.createGain();
  49     gainNode.gain.value = gain;
  50
  51     source.connect(gainNode);
  52     gainNode.connect(context.destination);
  53
  54     source.start(time);
  55 }
  56
  57 function init() {
  58     if (!window.testRunner)
  59         return;
  60
  61     // Create offline audio context.
  62     context = new OfflineAudioContext(2, sampleRate * lengthInSeconds, sampleRate);
  63
  64     // Create a buffer for a short "note".
  65     sinWaveBuffer = createSinWaveBuffer(bufferDurationSeconds, 880.0);
  66
  67     // Render 11 notes, starting at a gain of 1.0, decreasing in gain by 0.1.
  68     // The last note will be of gain 0.0, so shouldn't be perceptible in the rendered output.
  69     for (var i = 0; i < numberOfNotes; ++i) {
  70         var time = i * noteSpacing;
  71         var gain = 1.0 - i / (numberOfNotes - 1);
  72         playNote(time, gain);
  73     }
  74
  75     context.oncomplete = finishAudioTest;
  76     context.startRendering();
  77
  78     testRunner.waitUntilDone();
  79 }
  80
  81 </script>
  82
  83 </body>
  84 </html>