third_party/WebKit/LayoutTests/webaudio/osc-low-freq.html

   1 <!doctype html>
   2 <html>
   3   <head>
   4     <title>Test Custom Oscillator at Very Low Frequency</title>
   5     <script src="../resources/js-test.js"></script>
   6     <script src="resources/compatibility.js"></script>
   7     <script src="resources/audio-testing.js"></script>
   8   </head>
   9
  10   <body>
  11     <script>
  12       description("Test Custom Oscillator at Very Low Frequency");
  13       window.jsTestIsAsync = true;
  14
  15       // Create a custom oscillator and verify that the parts of a periodic wave that should be
  16       // ignored really are ignored.
  17
  18       var sampleRate = 48000;
  19
  20       // The desired frequency of the oscillator.  The value to be used depends on the
  21       // implementation of the PeriodicWave and should be less than then lowest fundamental
  22       // frequency. The lowest frequency is the Nyquist frequency divided by the max number of
  23       // coefficients used for the FFT. In the current implementation, the max number of
  24       // coefficients is 2048 (for a sample rate of 48 kHz) so the lowest frequency is 24000/2048 =
  25       // 11.78 Hz.
  26       var desiredFrequencyHz = 1;
  27
  28       // Minimum allowed SNR between the actual oscillator and the expected result.  Experimentally
  29       // determined.
  30       var snrThreshold = 130;
  31
  32       var context;
  33       var osc;
  34       var actual;
  35
  36       var audit = Audit.createTaskRunner();
  37
  38       // Compute the SNR between the actual result and expected cosine wave
  39       function checkCosineResult(result, freq, sampleRate) {
  40         var signal = 0;
  41         var noise = 0;
  42         var omega = 2 * Math.PI * freq / sampleRate;
  43
  44         actual = result.getChannelData(0);
  45
  46         for (var k = 0; k < actual.length; ++k) {
  47           var x = Math.cos(omega * k);
  48           var diff = x - actual[k];
  49           signal += x * x;
  50           noise += diff * diff;
  51         }
  52
  53         var snr = 10 * Math.log10(signal / noise);
  54
  55         Should("SNR of " + desiredFrequencyHz + " Hz sine wave", snr).beGreaterThanOrEqualTo(snrThreshold);
  56         testPassed("PeriodicWave coefficients that must be ignored were correctly ignored.");
  57       }
  58
  59       function runTest() {
  60         context = new OfflineAudioContext(1, sampleRate, sampleRate);
  61         osc = context.createOscillator();
  62
  63         // Create the custom oscillator.  For simplicity of testing, we use just a cosine wave, but
  64         // the initial elements of the real and imaginary parts are explicitly set to non-zero to
  65         // test that they are ignored.
  66         var r = new Float32Array(2);
  67         var i = new Float32Array(2);
  68         r[0] = 1; // DC component to be ignored
  69         r[1] = 1; // Fundamental
  70         i[0] = 1; // Sine term that doesn't actually exist in a Fourier series
  71         i[1] = 0;
  72         var wave = context.createPeriodicWave(r, i);
  73
  74         osc.setPeriodicWave(wave);
  75         osc.frequency.value = desiredFrequencyHz;
  76         osc.connect(context.destination);
  77         osc.start();
  78         context.startRendering().then(function (buffer) {
  79           checkCosineResult(buffer, desiredFrequencyHz, sampleRate);
  80         }).then(finishJSTest);
  81       };
  82
  83       runTest();
  84       successfullyParsed = true;
  85     </script>
  86   </body>
  87 </html>