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87 lines
3.1 KiB
HTML
87 lines
3.1 KiB
HTML
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<!DOCTYPE html>
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<title>Test effect of band limiting on PeriodicWave signals</title>
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<script src="/resources/testharness.js"></script>
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<script src="/resources/testharnessreport.js"></script>
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<script>
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const sampleRate = 48000;
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const bufferSize = 12800;
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const epsilon = 0.01;
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// "All implementations must support arrays up to at least 8192", but the
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// linear interpolation of the current implementation distorts the higher
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// frequency components too much to pass this test.
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const frequencyIndexMax = 200;
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// A set of oscillators are created near the Nyquist frequency.
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// These are factors giving each oscillator frequency relative to the Nyquist.
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// The first is an octave below Nyquist and the last is just above.
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const OCTAVE_BELOW = 0;
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const HALF_BELOW = 1;
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const NEAR_BELOW = 2;
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const ABOVE = 3;
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const oscillatorFactors = [0.5, Math.sqrt(0.5), 0.99, 1.01];
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const oscillatorCount = oscillatorFactors.length;
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// Return magnitude relative to unit sine wave
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function magnitude(array) {
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var mag = 0
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for (var i = 0; i < array.length; ++i) {
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sample = array[i];
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mag += sample * sample;
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}
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return Math.sqrt(2 * mag / array.length);
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}
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function test_frequency_index(frequencyIndex) {
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var context =
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new OfflineAudioContext(oscillatorCount, bufferSize, sampleRate);
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var merger = context.createChannelMerger(oscillatorCount);
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merger.connect(context.destination);
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var real = new Float32Array(frequencyIndex + 1);
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real[frequencyIndex] = 1;
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var image = new Float32Array(real.length);
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var wave = context.createPeriodicWave(real, image);
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for (var i = 0; i < oscillatorCount; ++i) {
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var oscillator = context.createOscillator();
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oscillator.frequency.value =
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oscillatorFactors[i] * sampleRate / (2 * frequencyIndex);
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oscillator.connect(merger, 0, i);
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oscillator.setPeriodicWave(wave);
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oscillator.start(0);
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}
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return context.startRendering().
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then((buffer) => {
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assert_equals(buffer.numberOfChannels, oscillatorCount);
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var magnitudes = [];
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for (var i = 0; i < oscillatorCount; ++i) {
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magnitudes[i] = magnitude(buffer.getChannelData(i));
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}
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// Unaffected by band-limiting one octave below Nyquist.
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assert_approx_equals(magnitudes[OCTAVE_BELOW], 1, epsilon,
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"magnitude with frequency octave below Nyquist");
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// Still at least half the amplitude at half octave below Nyquist.
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assert_greater_than(magnitudes[HALF_BELOW], 0.5 * (1 - epsilon),
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"magnitude with frequency half octave below Nyquist");
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// Approaching zero or zero near Nyquist.
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assert_less_than(magnitudes[NEAR_BELOW], 0.1,
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"magnitude with frequency near Nyquist");
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assert_equals(magnitudes[ABOVE], 0,
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"magnitude with frequency above Nyquist");
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});
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}
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// The 5/4 ratio with rounding up provides sampling across a range of
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// octaves and offsets within octaves.
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for (var frequencyIndex = 1;
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frequencyIndex < frequencyIndexMax;
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frequencyIndex = Math.floor((5 * frequencyIndex + 3) / 4)) {
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promise_test(test_frequency_index.bind(null, frequencyIndex),
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"Frequency " + frequencyIndex);
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}
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</script>
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