LayoutTests/webaudio/Oscillator/start-sampling.html - WebKit - Git at Google

 <!DOCTYPE html>
 <html>
   <head>
     <title>
       Test Sampling of Oscillator Start Times
     </title>
     <script src="../../imported/w3c/web-platform-tests/resources/testharness.js"></script>
     <script src="../../resources/testharnessreport.js"></script>
     <script src="../resources/audit-util.js"></script>
     <script src="../resources/audit.js"></script>
   </head>
   <body>
     <script id="layout-test-code">
       // Experimentation indicates that this sample rate with a 440 Hz
       // oscillator makes for a large difference in the difference signal if the
       // oscillator start isn't sampled correctly.
       let defaultSampleRate = 24000;
       let renderDuration = 1;
       let renderFrames = renderDuration * defaultSampleRate;

       let audit = Audit.createTaskRunner();

       audit.define(
           {
             label: 'basic test small',
             description: 'Start oscillator slightly past a sample frame'
           },
           function(task, should) {
             testStartSampling(should, 1.25, {
               error: 1.0880e-4,
               snrThreshold: 84.054
             }).then(task.done.bind(task));
           });

       audit.define(
           {
             label: 'basic test big',
             description: 'Start oscillator slightly before a sample frame'
           },
           function(task, should) {
             testStartSampling(should, 1.75, {
               error: 1.0844e-4,
               snrThreshold: 84.056
             }).then(task.done.bind(task));
           });

       audit.define(
           {
             label: 'diff big offset',
             description:
                 'Test sampling with start offset greater than 1/2 sampling frame'
           },
           function(task, should) {
             // With a sample rate of 24000 Hz, and an oscillator frequency of
             // 440 Hz (the default), a quarter wave delay is 13.636363...
             // frames.  This tests the case where the starting time is more than
             // 1/2 frame from the preceding sampling frame.  This tests one path
             // of the internal implementation.
             testStartWithGain(should, defaultSampleRate, {
               error: 1.9521e-6,
               snrThreshold: 128.12
             }).then(task.done.bind(task));
           });

       audit.define(
           {
             label: 'diff small offset',
             description:
                 'Test sampling with start offset less than 1/2 sampling frame'
           },
           function(task, should) {
             // With a sample rate of 48000 Hz, and an oscillator frequency of
             // 440 Hz (the default), a quarter wave delay is 27.2727... frames.
             // This tests the case where the starting time is less than 1/2
             // frame from the preceding sampling frame.  This tests one path of
             // the internal implementation.
             testStartWithGain(should, 48000, {
               error: 1.9521e-6,
               snrThreshold: 122.92
             }).then(task.done.bind(task));
           });

       function testStartSampling(should, startFrame, thresholds) {
         // Start the oscillator in the middle of a sample frame and compare
         // against the theoretical result.
         let context =
             new OfflineAudioContext(1, renderFrames, defaultSampleRate);
         let osc = context.createOscillator();
         osc.connect(context.destination);
         osc.start(startFrame / context.sampleRate);

         return context.startRendering().then(function(result) {
           let actual = result.getChannelData(0);
           let expected = new Array(actual.length);
           expected.fill(0);

           // The expected curve is
           //
           //   sin(2*pi*f*(t-t0))
           //
           // where f is the oscillator frequency and t0 is the start time.
           let actualStart = Math.ceil(startFrame);
           let omega = 2 * Math.PI * osc.frequency.value / context.sampleRate;
           for (let k = actualStart; k < actual.length; ++k) {
             expected[k] = Math.sin(omega * (k - startFrame));
           }

           let prefix = 'Oscillator.start(' + startFrame + ' frames)';
           should(actual, prefix).beCloseToArray(expected, {
             absoluteThreshold: thresholds.error
           });
           let snr = 10 * Math.log10(computeSNR(actual, expected));
           should(snr, prefix + ': SNR (dB)')
               .beGreaterThanOrEqualTo(thresholds.snrThreshold);
         })
       }

       function testStartWithGain(should, sampleRate, thresholds) {
         // Test consists of starting a cosine wave with a quarter wavelength
         // delay and comparing that with a sine wave that has the initial
         // quarter wavelength zeroed out.  These should be equal.

         let context = new OfflineAudioContext(3, renderFrames, sampleRate);
         let osc = context.createOscillator();

         let merger = context.createChannelMerger(3);
         merger.connect(context.destination);

         // Start the cosine oscillator at this time.  This means the wave starts
         // at frame 13.636363....
         let quarterWaveTime = (1 / 4) / osc.frequency.value;

         // Sine wave oscillator with gain term to zero out the initial quarter
         // wave length of the output.
         let g = context.createGain();
         g.gain.setValueAtTime(0, 0);
         g.gain.setValueAtTime(1, quarterWaveTime);
         osc.connect(g);
         g.connect(merger, 0, 2);
         g.connect(merger, 0, 0);

         // Cosine wave oscillator with starting after a quarter wave length.
         let osc2 = context.createOscillator();
         // Creates a cosine wave.
         let wave = context.createPeriodicWave(
             Float32Array.from([0, 1]), Float32Array.from([0, 0]));
         osc2.setPeriodicWave(wave);

         osc2.connect(merger, 0, 1);

         // A gain inverter so subtract the two waveforms.
         let inverter = context.createGain();
         inverter.gain.value = -1;
         osc2.connect(inverter);
         inverter.connect(merger, 0, 0);

         osc.start();
         osc2.start(quarterWaveTime);

         return context.startRendering().then(function(result) {
           // Channel 0 = diff
           // Channel 1 = osc with start
           // Channel 2 = osc with gain

           // Channel 0 should be very close to 0.
           // Channel 1 should match channel 2 very closely.
           let diff = result.getChannelData(0);
           let oscStart = result.getChannelData(1);
           let oscGain = result.getChannelData(2);
           let snr = 10 * Math.log10(computeSNR(oscStart, oscGain));

           let prefix =
               'Sample rate ' + sampleRate + ': Delayed cosine oscillator';
           should(oscStart, prefix).beCloseToArray(oscGain, {
             absoluteThreshold: thresholds.error
           });
           should(snr, prefix + ': SNR (dB)')
               .beGreaterThanOrEqualTo(thresholds.snrThreshold);
         });
       }

       audit.run();
     </script>
   </body>
 </html>
	<!DOCTYPE html>
	<html>
	<head>
	<title>
	Test Sampling of Oscillator Start Times
	</title>
	<script src="../../imported/w3c/web-platform-tests/resources/testharness.js"></script>
	<script src="../../resources/testharnessreport.js"></script>
	<script src="../resources/audit-util.js"></script>
	<script src="../resources/audit.js"></script>
	</head>
	<body>
	<script id="layout-test-code">
	// Experimentation indicates that this sample rate with a 440 Hz
	// oscillator makes for a large difference in the difference signal if the
	// oscillator start isn't sampled correctly.
	let defaultSampleRate = 24000;
	let renderDuration = 1;
	let renderFrames = renderDuration * defaultSampleRate;

	let audit = Audit.createTaskRunner();

	audit.define(
	{
	label: 'basic test small',
	description: 'Start oscillator slightly past a sample frame'
	},
	function(task, should) {
	testStartSampling(should, 1.25, {
	error: 1.0880e-4,
	snrThreshold: 84.054
	}).then(task.done.bind(task));
	});

	audit.define(
	{
	label: 'basic test big',
	description: 'Start oscillator slightly before a sample frame'
	},
	function(task, should) {
	testStartSampling(should, 1.75, {
	error: 1.0844e-4,
	snrThreshold: 84.056
	}).then(task.done.bind(task));
	});

	audit.define(
	{
	label: 'diff big offset',
	description:
	'Test sampling with start offset greater than 1/2 sampling frame'
	},
	function(task, should) {
	// With a sample rate of 24000 Hz, and an oscillator frequency of
	// 440 Hz (the default), a quarter wave delay is 13.636363...
	// frames. This tests the case where the starting time is more than
	// 1/2 frame from the preceding sampling frame. This tests one path
	// of the internal implementation.
	testStartWithGain(should, defaultSampleRate, {
	error: 1.9521e-6,
	snrThreshold: 128.12
	}).then(task.done.bind(task));
	});

	audit.define(
	{
	label: 'diff small offset',
	description:
	'Test sampling with start offset less than 1/2 sampling frame'
	},
	function(task, should) {
	// With a sample rate of 48000 Hz, and an oscillator frequency of
	// 440 Hz (the default), a quarter wave delay is 27.2727... frames.
	// This tests the case where the starting time is less than 1/2
	// frame from the preceding sampling frame. This tests one path of
	// the internal implementation.
	testStartWithGain(should, 48000, {
	error: 1.9521e-6,
	snrThreshold: 122.92
	}).then(task.done.bind(task));
	});

	function testStartSampling(should, startFrame, thresholds) {
	// Start the oscillator in the middle of a sample frame and compare
	// against the theoretical result.
	let context =
	new OfflineAudioContext(1, renderFrames, defaultSampleRate);
	let osc = context.createOscillator();
	osc.connect(context.destination);
	osc.start(startFrame / context.sampleRate);

	return context.startRendering().then(function(result) {
	let actual = result.getChannelData(0);
	let expected = new Array(actual.length);
	expected.fill(0);

	// The expected curve is
	//
	// sin(2pif*(t-t0))
	//
	// where f is the oscillator frequency and t0 is the start time.
	let actualStart = Math.ceil(startFrame);
	let omega = 2 * Math.PI * osc.frequency.value / context.sampleRate;
	for (let k = actualStart; k < actual.length; ++k) {
	expected[k] = Math.sin(omega * (k - startFrame));
	}

	let prefix = 'Oscillator.start(' + startFrame + ' frames)';
	should(actual, prefix).beCloseToArray(expected, {
	absoluteThreshold: thresholds.error
	});
	let snr = 10 * Math.log10(computeSNR(actual, expected));
	should(snr, prefix + ': SNR (dB)')
	.beGreaterThanOrEqualTo(thresholds.snrThreshold);
	})
	}

	function testStartWithGain(should, sampleRate, thresholds) {
	// Test consists of starting a cosine wave with a quarter wavelength
	// delay and comparing that with a sine wave that has the initial
	// quarter wavelength zeroed out. These should be equal.

	let context = new OfflineAudioContext(3, renderFrames, sampleRate);
	let osc = context.createOscillator();

	let merger = context.createChannelMerger(3);
	merger.connect(context.destination);

	// Start the cosine oscillator at this time. This means the wave starts
	// at frame 13.636363....
	let quarterWaveTime = (1 / 4) / osc.frequency.value;

	// Sine wave oscillator with gain term to zero out the initial quarter
	// wave length of the output.
	let g = context.createGain();
	g.gain.setValueAtTime(0, 0);
	g.gain.setValueAtTime(1, quarterWaveTime);
	osc.connect(g);
	g.connect(merger, 0, 2);
	g.connect(merger, 0, 0);

	// Cosine wave oscillator with starting after a quarter wave length.
	let osc2 = context.createOscillator();
	// Creates a cosine wave.
	let wave = context.createPeriodicWave(
	Float32Array.from([0, 1]), Float32Array.from([0, 0]));
	osc2.setPeriodicWave(wave);

	osc2.connect(merger, 0, 1);

	// A gain inverter so subtract the two waveforms.
	let inverter = context.createGain();
	inverter.gain.value = -1;
	osc2.connect(inverter);
	inverter.connect(merger, 0, 0);

	osc.start();
	osc2.start(quarterWaveTime);

	return context.startRendering().then(function(result) {
	// Channel 0 = diff
	// Channel 1 = osc with start
	// Channel 2 = osc with gain

	// Channel 0 should be very close to 0.
	// Channel 1 should match channel 2 very closely.
	let diff = result.getChannelData(0);
	let oscStart = result.getChannelData(1);
	let oscGain = result.getChannelData(2);
	let snr = 10 * Math.log10(computeSNR(oscStart, oscGain));

	let prefix =
	'Sample rate ' + sampleRate + ': Delayed cosine oscillator';
	should(oscStart, prefix).beCloseToArray(oscGain, {
	absoluteThreshold: thresholds.error
	});
	should(snr, prefix + ': SNR (dB)')
	.beGreaterThanOrEqualTo(thresholds.snrThreshold);
	});
	}

	audit.run();
	</script>
	</body>
	</html>