| <!doctype html> |
| <html> |
| <head> |
| <title>Test Custom Oscillator at Very Low Frequency</title> |
| <script src="../resources/js-test.js"></script> |
| <script src="resources/compatibility.js"></script> |
| <script src="resources/audio-testing.js"></script> |
| </head> |
| |
| <body> |
| <script> |
| description("Test Custom Oscillator at Very Low Frequency"); |
| window.jsTestIsAsync = true; |
| |
| // Create a custom oscillator and verify that the parts of a periodic wave that should be |
| // ignored really are ignored. |
| |
| var 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. |
| var desiredFrequencyHz = 1; |
| |
| // Minimum allowed SNR between the actual oscillator and the expected result. Experimentally |
| // determined. |
| var snrThreshold = 130; |
| |
| var context; |
| var osc; |
| var actual; |
| |
| var audit = Audit.createTaskRunner(); |
| |
| // Compute the SNR between the actual result and expected cosine wave |
| function checkCosineResult(result, freq, sampleRate) { |
| var signal = 0; |
| var noise = 0; |
| var omega = 2 * Math.PI * freq / sampleRate; |
| |
| actual = result.getChannelData(0); |
| |
| for (var k = 0; k < actual.length; ++k) { |
| var x = Math.cos(omega * k); |
| var diff = x - actual[k]; |
| signal += x * x; |
| noise += diff * diff; |
| } |
| |
| var snr = 10 * Math.log10(signal / noise); |
| |
| Should("SNR of " + desiredFrequencyHz + " Hz sine wave", snr).beGreaterThanOrEqualTo(snrThreshold); |
| testPassed("PeriodicWave coefficients that must be ignored were correctly ignored."); |
| } |
| |
| function runTest() { |
| 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. |
| var r = new Float32Array(2); |
| var 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; |
| var wave = context.createPeriodicWave(r, i); |
| |
| osc.setPeriodicWave(wave); |
| osc.frequency.value = desiredFrequencyHz; |
| osc.connect(context.destination); |
| osc.start(); |
| context.startRendering().then(function (buffer) { |
| checkCosineResult(buffer, desiredFrequencyHz, sampleRate); |
| }).then(finishJSTest); |
| }; |
| |
| runTest(); |
| successfullyParsed = true; |
| </script> |
| </body> |
| </html> |
