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<title>Test BiquadFilterNode All Pass Filter</title>
<script src="/tests/SimpleTest/SimpleTest.js"></script>
<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
<pre id="test">
<script src="audio-testing.js"></script>
<script src="biquad-filters.js"></script>
<script src="biquad-testing.js"></script>
<script src="webaudio.js" type="text/javascript"></script>
<script class="testbody" type="text/javascript">
addLoadEvent(function() {
// A high sample rate shows the issue more clearly.
var sampleRate = 192000;
// Some short duration because we don't need to run the test for very long.
var testDurationSec = 0.5;
var testDurationFrames = testDurationSec * sampleRate;
// Amplitude experimentally determined to give a biquad output close to 1. (No attempt was
// made to produce exactly 1; it's not needed.)
var sourceAmplitude = 100;
// The output of the biquad filter should not change by more than this much between output
// samples. Threshold was determined experimentally.
var glitchThreshold = 0.01292;
// Test that a Biquad filter doesn't have it's output terminated because the input has gone
// away. Generally, when a source node is finished, it disconnects itself from any downstream
// nodes. This is the correct behavior. Nodes that have no inputs (disconnected) are
// generally assumed to output zeroes. This is also desired behavior. However, biquad
// filters have memory so they should not suddenly output zeroes when the input is
// disconnected. This test checks to see if the output doesn't suddenly change to zero.
var context = new OfflineAudioContext(1, testDurationFrames, sampleRate);
// Create an impulse source.
var buffer = context.createBuffer(1, 1, context.sampleRate);
buffer.getChannelData(0)[0] = sourceAmplitude;
var source = context.createBufferSource();
source.buffer = buffer;
// Create the biquad filter. It doesn't really matter what kind, so the default filter type
// and parameters is fine. Connect the source to it.
var biquad = context.createBiquadFilter();
context.startRendering().then(function(result) {
// There should be no large discontinuities in the output
var buffer = result.getChannelData(0);
var maxGlitchIndex = 0;
var maxGlitchValue = 0.0;
for (var i = 1; i < buffer.length; i++) {
var diff = Math.abs(buffer[i-1] - buffer[i]);
if (diff >= glitchThreshold) {
if (diff > maxGlitchValue) {
maxGlitchIndex = i;
maxGlitchValue = diff;
ok(maxGlitchIndex == 0, 'glitches detected in biquad output: maximum glitch at ' + maxGlitchIndex + ' with diff of ' + maxGlitchValue);