| OLD | NEW |
|---|
| 1 // Notes about generated waveforms: | 1 // Notes about generated waveforms: |
| 2 // | 2 // |
| 3 // QUESTION: Why does the wave shape not look like the exact shape (sharp edges)
? | 3 // QUESTION: Why does the wave shape not look like the exact shape (sharp edges)
? |
| 4 // ANSWER: Because a shape with sharp edges has infinitely high frequency conten
t. | 4 // ANSWER: Because a shape with sharp edges has infinitely high frequency conten
t. |
| 5 // Since a digital audio signal must be band-limited based on the nyquist freque
ncy (half the sample-rate) | 5 // Since a digital audio signal must be band-limited based on the nyquist freque
ncy (half the sample-rate) |
| 6 // in order to avoid aliasing, this creates more rounded edges and "ringing" in
the | 6 // in order to avoid aliasing, this creates more rounded edges and "ringing" in
the |
| 7 // appearance of the waveform. See Nyquist-Shannon sampling theorem: | 7 // appearance of the waveform. See Nyquist-Shannon sampling theorem: |
| 8 // http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem | 8 // http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem |
| 9 // | 9 // |
| 10 // QUESTION: Why does the very end of the generated signal appear to get slightl
y weaker? | 10 // QUESTION: Why does the very end of the generated signal appear to get slightl
y weaker? |
| 11 // ANSWER: This is an artifact of the algorithm to avoid aliasing. | 11 // ANSWER: This is an artifact of the algorithm to avoid aliasing. |
| 12 // |
| 13 // QUESTION: Since the tests compare the actual result with an expected referenc
e file, how are the |
| 14 // reference files created? |
| 15 // ANSWER: Create an html with the following contents in the webaudio directory.
Then run a layout |
| 16 // test on this file. A new file names "<file>-actual.wav" is created that cont
ains the new result |
| 17 // that can be used as the new expected reference file. Replace the "sine" belo
w with the |
| 18 // oscillator type that you want to use. |
| 19 // |
| 20 // <!DOCTYPE html> |
| 21 // <html> |
| 22 // <head> |
| 23 // <script type="text/javascript" src="resources/audio-testing.js"></script> |
| 24 // <script type="text/javascript" src="resources/oscillator-testing.js"></script
> |
| 25 // </head> |
| 26 // <body> |
| 27 // <script> |
| 28 // window.onload = init; |
| 29 // |
| 30 // function init() { |
| 31 // if (!window.testRunner) |
| 32 // return; |
| 33 // |
| 34 // context = new OfflineAudioContext(1, sampleRate * lengthInSeconds, sample
Rate); |
| 35 // generateExponentialOscillatorSweep(context, "sine"); |
| 36 // |
| 37 // context.oncomplete = finishAudioTest; |
| 38 // context.startRendering(); |
| 39 // |
| 40 // testRunner.waitUntilDone(); |
| 41 // } |
| 42 // |
| 43 // </script> |
| 44 // </body> |
| 45 // </html> |
| 12 | 46 |
| 13 var sampleRate = 44100.0; | 47 var sampleRate = 44100.0; |
| 14 var nyquist = 0.5 * sampleRate; | 48 var nyquist = 0.5 * sampleRate; |
| 15 var lengthInSeconds = 4; | 49 var lengthInSeconds = 4; |
| 16 var lowFrequency = 10; | 50 var lowFrequency = 10; |
| 17 var highFrequency = nyquist + 2000; // go slightly higher than nyquist to make s
ure we generate silence there | 51 var highFrequency = nyquist + 2000; // go slightly higher than nyquist to make s
ure we generate silence there |
| 18 var context = 0; | 52 var context = 0; |
| 19 | 53 |
| 54 // Mostly for debugging |
| 55 |
| 56 // An AudioBuffer for the reference (expected) result. |
| 57 var reference = 0; |
| 58 |
| 59 // The actual rendered data produced by the test. |
| 60 var renderedData = 0; |
| 61 |
| 62 // Signal power of the reference |
| 63 var signalPower = 0; |
| 64 |
| 65 // Noise power of the difference between the reference and actual result. |
| 66 var noisePower = 0; |
| 67 |
| 20 function generateExponentialOscillatorSweep(context, oscillatorType) { | 68 function generateExponentialOscillatorSweep(context, oscillatorType) { |
| 21 var osc = context.createOscillator(); | 69 var osc = context.createOscillator(); |
| 22 if (oscillatorType == "custom") { | 70 if (oscillatorType == "custom") { |
| 23 // Create a simple waveform with three Fourier coefficients. | 71 // Create a simple waveform with three Fourier coefficients. |
| 24 // Note the first values are expected to be zero (DC for coeffA and Nyqu
ist for coeffB). | 72 // Note the first values are expected to be zero (DC for coeffA and Nyqu
ist for coeffB). |
| 25 var coeffA = new Float32Array([0, 1, 0.5]); | 73 var coeffA = new Float32Array([0, 1, 0.5]); |
| 26 var coeffB = new Float32Array([0, 0, 0]); | 74 var coeffB = new Float32Array([0, 0, 0]); |
| 27 var wave = context.createPeriodicWave(coeffA, coeffB); | 75 var wave = context.createPeriodicWave(coeffA, coeffB); |
| 28 osc.setPeriodicWave(wave); | 76 osc.setPeriodicWave(wave); |
| 29 } else { | 77 } else { |
| 30 osc.type = oscillatorType; | 78 osc.type = oscillatorType; |
| 31 } | 79 } |
| 32 | 80 |
| 33 // Scale by 1/2 to better visualize the waveform and to avoid clipping past
full scale. | 81 // Scale by 1/2 to better visualize the waveform and to avoid clipping past
full scale. |
| 34 var gainNode = context.createGain(); | 82 var gainNode = context.createGain(); |
| 35 gainNode.gain.value = 0.5; | 83 gainNode.gain.value = 0.5; |
| 36 osc.connect(gainNode); | 84 osc.connect(gainNode); |
| 37 gainNode.connect(context.destination); | 85 gainNode.connect(context.destination); |
| 38 | 86 |
| 39 osc.start(0); | 87 osc.start(0); |
| 40 | 88 |
| 41 var nyquist = 0.5 * sampleRate; | 89 var nyquist = 0.5 * sampleRate; |
| 42 osc.frequency.setValueAtTime(10, 0); | 90 osc.frequency.setValueAtTime(10, 0); |
| 43 osc.frequency.exponentialRampToValueAtTime(highFrequency, lengthInSeconds); | 91 osc.frequency.exponentialRampToValueAtTime(highFrequency, lengthInSeconds); |
| 44 } | 92 } |
| 93 |
| 94 function calculateSNR(sPower, nPower) |
| 95 { |
| 96 if (nPower == 0 && sPower > 0) { |
| 97 return 1000; |
| 98 } |
| 99 return 10 * Math.log10(sPower / nPower); |
| 100 } |
| 101 |
| 102 function loadReferenceAndRunTest(oscType) { |
| 103 var bufferLoader = new BufferLoader( |
| 104 context, |
| 105 [ "oscillator-" + oscType + "-expected.wav" ], |
| 106 function (bufferList) { |
| 107 reference = bufferList[0].getChannelData(0); |
| 108 generateExponentialOscillatorSweep(context, oscType); |
| 109 context.oncomplete = checkResult; |
| 110 context.startRendering(); |
| 111 }); |
| 112 |
| 113 bufferLoader.load(); |
| 114 } |
| 115 |
| 116 function checkResult (event) { |
| 117 renderedData = event.renderedBuffer.getChannelData(0); |
| 118 // Compute signal to noise ratio between the result and the reference. Also
keep track |
| 119 // of the max difference (and position). |
| 120 |
| 121 var maxError = -1; |
| 122 var errorPosition = -1; |
| 123 var diffCount = 0; |
| 124 |
| 125 for (var k = 0; k < renderedData.length; ++k) { |
| 126 var diff = renderedData[k] - reference[k]; |
| 127 noisePower += diff * diff; |
| 128 signalPower += reference[k] * reference[k]; |
| 129 if (Math.abs(diff) > maxError) { |
| 130 maxError = Math.abs(diff); |
| 131 errorPosition = k; |
| 132 } |
| 133 // The reference file is a 16-bit WAV file, so we will never get an exac
t match |
| 134 // between it and the actual floating-point result. |
| 135 if (diff > 1/waveScaleFactor) { |
| 136 diffCount++; |
| 137 } |
| 138 } |
| 139 |
| 140 var snr = calculateSNR(signalPower, noisePower); |
| 141 if (snr < thresholdSNR) { |
| 142 testFailed("Expected SNR of " + thresholdSNR + " dB, but actual SNR is "
+ snr + " dB"); |
| 143 } else { |
| 144 testPassed("Exceeded SNR threshold of " + thresholdSNR + " dB"); |
| 145 } |
| 146 |
| 147 if (maxError > thresholdDiff) { |
| 148 testFailed("Maximum difference of " + (maxError * waveScaleFactor) + " a
t " |
| 149 + errorPosition + " exceeded threshold of " + (thresholdDiff
* waveScaleFactor) |
| 150 + " ulp (16-bits)"); |
| 151 } else { |
| 152 testPassed("Maximum difference below threshold of " |
| 153 + (thresholdDiff * waveScaleFactor) + " ulp (16-bits)"); |
| 154 } |
| 155 if (diffCount > thresholdDiffCount) { |
| 156 testFailed(diffCount + " differences found but expected no more than " +
thresholdDiffCount); |
| 157 } else { |
| 158 testPassed("Number of differences between actual and expected result is
less than " + thresholdDiffCount); |
| 159 } |
| 160 |
| 161 finishJSTest(); |
| 162 } |
| 163 |
| 164 |
| OLD | NEW |
|---|
Chromium Code Reviews
Issue 720293002:
Replace oscillator tests with more robust tests (Closed)
Base URL: svn://svn.chromium.org/blink/trunk