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<!DOCTYPE html>
<html>
<head>
<script src="../resources/js-test-pre.js"></script>
<script type="text/javascript" src="resources/audio-testing.js"></script>
<script type="text/javascript" src="resources/buffer-loader.js"></script>
</head>
<body>
<div id="description"></div>
<div id="console"></div>
<script>
description("Tests that WaveShaperNode applies proper non-linear distortion.");
var sampleRate = 44100;
var lengthInSeconds = 4;
var numberOfRenderFrames = sampleRate * lengthInSeconds;
var numberOfCurveFrames = 65536;
var inputBuffer;
var waveShapingCurve;
var context;
function generateInputBuffer() {
// Create mono input buffer.
var buffer = context.createBuffer(1, numberOfRenderFrames, context.sampleRate);
var data = buffer.getChannelData(0);
// Generate an input vector with values from -1 -> +1 over a duration of lengthInSeconds.
// This exercises the full nominal input range and will touch every point of the shaping curve.
for (var i = 0; i < numberOfRenderFrames; ++i) {
var x = i / numberOfRenderFrames; // 0 -> 1
x = 2 * x - 1; // -1 -> +1
data[i] = x;
}
return buffer;
}
// Generates a symmetric curve: Math.atan(5 * x) / (0.5 * Math.PI)
// (with x == 0 corresponding to the center of the array)
// This curve is arbitrary, but would be useful in the real-world.
// To some extent, the actual curve we choose is not important in this test,
// since the input vector walks through all possible curve values.
function generateWaveShapingCurve() {
var curve = new Float32Array(numberOfCurveFrames);
var n = numberOfCurveFrames;
var n2 = n / 2;
for (var i = 0; i < n; ++i) {
var x = (i - n2) / n2;
var y = Math.atan(5 * x) / (0.5 * Math.PI);
}
return curve;
}
function checkShapedCurve(event) {
var buffer = event.renderedBuffer;
var inputData = inputBuffer.getChannelData(0);
var outputData = buffer.getChannelData(0);
var success = true;
// Go through every sample and make sure it has been shaped exactly according to the shaping curve we gave it.
for (var i = 0; i < buffer.length; ++i) {
var input = inputData[i];
// Calculate an index based on input -1 -> +1 with 0 being at the center of the curve data.
var index = Math.floor(numberOfCurveFrames * 0.5 * (input + 1));
// Clip index to the input range of the curve.
// This takes care of input outside of nominal range -1 -> +1
index = index < 0 ? 0 : index;
index = index > numberOfCurveFrames - 1 ? numberOfCurveFrames - 1 : index;
var expectedOutput = waveShapingCurve[index];
var output = outputData[i];
if (output != expectedOutput) {
success = false;
break;
}
}
if (success) {
testPassed("WaveShaperNode properly applied non-linear distortion.");
} else {
testFailed("WaveShaperNode did not properly apply non-linear distortion.");
}
finishJSTest();
}
function runTest() {
if (window.testRunner) {
testRunner.dumpAsText();
testRunner.waitUntilDone();
}
window.jsTestIsAsync = true;
// Create offline audio context.
context = new webkitOfflineAudioContext(1, numberOfRenderFrames, sampleRate);
// source -> waveshaper -> destination
var source = context.createBufferSource();
var waveshaper = context.createWaveShaper();
source.connect(waveshaper);
waveshaper.connect(context.destination);
// Create an input test vector.
inputBuffer = generateInputBuffer();
source.buffer = inputBuffer;
// We'll apply non-linear distortion according to this shaping curve.
waveShapingCurve = generateWaveShapingCurve();
waveshaper.curve = waveShapingCurve;
source.noteOn(0);
context.oncomplete = checkShapedCurve;
context.startRendering();
}
runTest();
</script>
<script src="../resources/js-test-post.js"></script>
</body>
</html>