| <!DOCTYPE html> |
| <html> |
| <head> |
| <title> |
| Test Custom Oscillator at Very Low Frequency |
| </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"> |
| // Create a custom oscillator and verify that the parts of a periodic wave |
| // that should be ignored really are ignored. |
| |
| let sampleRate = 48000; |
| |
| // The desired frequency of the oscillator. The value to be used depends |
| // on the implementation of the PeriodicWave and should be less than then |
| // lowest fundamental frequency. The lowest frequency is the Nyquist |
| // frequency divided by the max number of coefficients used for the FFT. |
| // In the current implementation, the max number of coefficients is 2048 |
| // (for a sample rate of 48 kHz) so the lowest frequency is 24000/2048 = |
| // 11.78 Hz. |
| let desiredFrequencyHz = 1; |
| |
| // Minimum allowed SNR between the actual oscillator and the expected |
| // result. Experimentally determined. |
| let snrThreshold = 130; |
| |
| let context; |
| let osc; |
| let actual; |
| |
| let audit = Audit.createTaskRunner(); |
| |
| // Compute the SNR between the actual result and expected cosine wave |
| function checkCosineResult(should, result, freq, sampleRate) { |
| let signal = 0; |
| let noise = 0; |
| let omega = 2 * Math.PI * freq / sampleRate; |
| |
| actual = result.getChannelData(0); |
| |
| for (let k = 0; k < actual.length; ++k) { |
| let x = Math.cos(omega * k); |
| let diff = x - actual[k]; |
| signal += x * x; |
| noise += diff * diff; |
| } |
| |
| let snr = 10 * Math.log10(signal / noise); |
| |
| should(snr, 'SNR of ' + desiredFrequencyHz + ' Hz sine wave') |
| .beGreaterThanOrEqualTo(snrThreshold); |
| } |
| |
| audit.define('low-freq-oscillator', (task, should) => { |
| context = new OfflineAudioContext(1, sampleRate, sampleRate); |
| osc = context.createOscillator(); |
| |
| // Create the custom oscillator. For simplicity of testing, we use just |
| // a cosine wave, but the initial elements of the real and imaginary |
| // parts are explicitly set to non-zero to test that they are ignored. |
| let r = new Float32Array(2); |
| let i = new Float32Array(2); |
| r[0] = 1; // DC component to be ignored |
| r[1] = 1; // Fundamental |
| i[0] = 1; // Sine term that doesn't actually exist in a Fourier series |
| i[1] = 0; |
| let wave = context.createPeriodicWave(r, i); |
| |
| osc.setPeriodicWave(wave); |
| osc.frequency.value = desiredFrequencyHz; |
| osc.connect(context.destination); |
| osc.start(); |
| context.startRendering() |
| .then(function(buffer) { |
| checkCosineResult(should, buffer, desiredFrequencyHz, sampleRate); |
| }) |
| .then(() => task.done()); |
| }); |
| |
| audit.run(); |
| </script> |
| </body> |
| </html> |
