new file mode 100644
--- /dev/null
+++ b/dom/media/webaudio/test/blink/biquad-filters.js
@@ -0,0 +1,370 @@
+// Taken from WebKit/LayoutTests/webaudio/resources/biquad-filters.js
+
+// A biquad filter has a z-transform of
+// H(z) = (b0 + b1 / z + b2 / z^2) / (1 + a1 / z + a2 / z^2)
+//
+// The formulas for the various filters were taken from
+// http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt.
+
+
+// Lowpass filter.
+function createLowpassFilter(freq, q, gain) {
+ var b0;
+ var b1;
+ var b2;
+ var a1;
+ var a2;
+
+ if (freq == 1) {
+ // The formula below works, except for roundoff. When freq = 1,
+ // the filter is just a wire, so hardwire the coefficients.
+ b0 = 1;
+ b1 = 0;
+ b2 = 0;
+ a1 = 0;
+ a2 = 0;
+ } else {
+ var g = Math.pow(10, q / 20);
+ var d = Math.sqrt((4 - Math.sqrt(16 - 16 / (g * g))) / 2);
+ var theta = Math.PI * freq;
+ var sn = d * Math.sin(theta) / 2;
+ var beta = 0.5 * (1 - sn) / (1 + sn);
+ var gamma = (0.5 + beta) * Math.cos(theta);
+ var alpha = 0.25 * (0.5 + beta - gamma);
+
+ b0 = 2 * alpha;
+ b1 = 4 * alpha;
+ b2 = 2 * alpha;
+ a1 = 2 * (-gamma);
+ a2 = 2 * beta;
+ }
+
+ return {b0 : b0, b1 : b1, b2 : b2, a1 : a1, a2 : a2};
+}
+
+function createHighpassFilter(freq, q, gain) {
+ var b0;
+ var b1;
+ var b2;
+ var a1;
+ var a2;
+
+ if (freq == 1) {
+ // The filter is 0
+ b0 = 0;
+ b1 = 0;
+ b2 = 0;
+ a1 = 0;
+ a2 = 0;
+ } else if (freq == 0) {
+ // The filter is 1. Computation of coefficients below is ok, but
+ // there's a pole at 1 and a zero at 1, so round-off could make
+ // the filter unstable.
+ b0 = 1;
+ b1 = 0;
+ b2 = 0;
+ a1 = 0;
+ a2 = 0;
+ } else {
+ var g = Math.pow(10, q / 20);
+ var d = Math.sqrt((4 - Math.sqrt(16 - 16 / (g * g))) / 2);
+ var theta = Math.PI * freq;
+ var sn = d * Math.sin(theta) / 2;
+ var beta = 0.5 * (1 - sn) / (1 + sn);
+ var gamma = (0.5 + beta) * Math.cos(theta);
+ var alpha = 0.25 * (0.5 + beta + gamma);
+
+ b0 = 2 * alpha;
+ b1 = -4 * alpha;
+ b2 = 2 * alpha;
+ a1 = 2 * (-gamma);
+ a2 = 2 * beta;
+ }
+
+ return {b0 : b0, b1 : b1, b2 : b2, a1 : a1, a2 : a2};
+}
+
+function normalizeFilterCoefficients(b0, b1, b2, a0, a1, a2) {
+ var scale = 1 / a0;
+
+ return {b0 : b0 * scale,
+ b1 : b1 * scale,
+ b2 : b2 * scale,
+ a1 : a1 * scale,
+ a2 : a2 * scale};
+}
+
+function createBandpassFilter(freq, q, gain) {
+ var b0;
+ var b1;
+ var b2;
+ var a0;
+ var a1;
+ var a2;
+ var coef;
+
+ if (freq > 0 && freq < 1) {
+ var w0 = Math.PI * freq;
+ if (q > 0) {
+ var alpha = Math.sin(w0) / (2 * q);
+ var k = Math.cos(w0);
+
+ b0 = alpha;
+ b1 = 0;
+ b2 = -alpha;
+ a0 = 1 + alpha;
+ a1 = -2 * k;
+ a2 = 1 - alpha;
+
+ coef = normalizeFilterCoefficients(b0, b1, b2, a0, a1, a2);
+ } else {
+ // q = 0, and frequency is not 0 or 1. The above formula has a
+ // divide by zero problem. The limit of the z-transform as q
+ // approaches 0 is 1, so set the filter that way.
+ coef = {b0 : 1, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ }
+ } else {
+ // When freq = 0 or 1, the z-transform is identically 0,
+ // independent of q.
+ coef = {b0 : 0, b1 : 0, b2 : 0, a1 : 0, a2 : 0}
+ }
+
+ return coef;
+}
+
+function createLowShelfFilter(freq, q, gain) {
+ // q not used
+ var b0;
+ var b1;
+ var b2;
+ var a0;
+ var a1;
+ var a2;
+ var coef;
+
+ var S = 1;
+ var A = Math.pow(10, gain / 40);
+
+ if (freq == 1) {
+ // The filter is just a constant gain
+ coef = {b0 : A * A, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ } else if (freq == 0) {
+ // The filter is 1
+ coef = {b0 : 1, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ } else {
+ var w0 = Math.PI * freq;
+ var alpha = 1 / 2 * Math.sin(w0) * Math.sqrt((A + 1 / A) * (1 / S - 1) + 2);
+ var k = Math.cos(w0);
+ var k2 = 2 * Math.sqrt(A) * alpha;
+ var Ap1 = A + 1;
+ var Am1 = A - 1;
+
+ b0 = A * (Ap1 - Am1 * k + k2);
+ b1 = 2 * A * (Am1 - Ap1 * k);
+ b2 = A * (Ap1 - Am1 * k - k2);
+ a0 = Ap1 + Am1 * k + k2;
+ a1 = -2 * (Am1 + Ap1 * k);
+ a2 = Ap1 + Am1 * k - k2;
+ coef = normalizeFilterCoefficients(b0, b1, b2, a0, a1, a2);
+ }
+
+ return coef;
+}
+
+function createHighShelfFilter(freq, q, gain) {
+ // q not used
+ var b0;
+ var b1;
+ var b2;
+ var a0;
+ var a1;
+ var a2;
+ var coef;
+
+ var A = Math.pow(10, gain / 40);
+
+ if (freq == 1) {
+ // When freq = 1, the z-transform is 1
+ coef = {b0 : 1, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ } else if (freq > 0) {
+ var w0 = Math.PI * freq;
+ var S = 1;
+ var alpha = 0.5 * Math.sin(w0) * Math.sqrt((A + 1 / A) * (1 / S - 1) + 2);
+ var k = Math.cos(w0);
+ var k2 = 2 * Math.sqrt(A) * alpha;
+ var Ap1 = A + 1;
+ var Am1 = A - 1;
+
+ b0 = A * (Ap1 + Am1 * k + k2);
+ b1 = -2 * A * (Am1 + Ap1 * k);
+ b2 = A * (Ap1 + Am1 * k - k2);
+ a0 = Ap1 - Am1 * k + k2;
+ a1 = 2 * (Am1 - Ap1*k);
+ a2 = Ap1 - Am1 * k-k2;
+
+ coef = normalizeFilterCoefficients(b0, b1, b2, a0, a1, a2);
+ } else {
+ // When freq = 0, the filter is just a gain
+ coef = {b0 : A * A, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ }
+
+ return coef;
+}
+
+function createPeakingFilter(freq, q, gain) {
+ var b0;
+ var b1;
+ var b2;
+ var a0;
+ var a1;
+ var a2;
+ var coef;
+
+ var A = Math.pow(10, gain / 40);
+
+ if (freq > 0 && freq < 1) {
+ if (q > 0) {
+ var w0 = Math.PI * freq;
+ var alpha = Math.sin(w0) / (2 * q);
+ var k = Math.cos(w0);
+
+ b0 = 1 + alpha * A;
+ b1 = -2 * k;
+ b2 = 1 - alpha * A;
+ a0 = 1 + alpha / A;
+ a1 = -2 * k;
+ a2 = 1 - alpha / A;
+
+ coef = normalizeFilterCoefficients(b0, b1, b2, a0, a1, a2);
+ } else {
+ // q = 0, we have a divide by zero problem in the formulas
+ // above. But if we look at the z-transform, we see that the
+ // limit as q approaches 0 is A^2.
+ coef = {b0 : A * A, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ }
+ } else {
+ // freq = 0 or 1, the z-transform is 1
+ coef = {b0 : 1, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ }
+
+ return coef;
+}
+
+function createNotchFilter(freq, q, gain) {
+ var b0;
+ var b1;
+ var b2;
+ var a0;
+ var a1;
+ var a2;
+ var coef;
+
+ if (freq > 0 && freq < 1) {
+ if (q > 0) {
+ var w0 = Math.PI * freq;
+ var alpha = Math.sin(w0) / (2 * q);
+ var k = Math.cos(w0);
+
+ b0 = 1;
+ b1 = -2 * k;
+ b2 = 1;
+ a0 = 1 + alpha;
+ a1 = -2 * k;
+ a2 = 1 - alpha;
+ coef = normalizeFilterCoefficients(b0, b1, b2, a0, a1, a2);
+ } else {
+ // When q = 0, we get a divide by zero above. The limit of the
+ // z-transform as q approaches 0 is 0, so set the coefficients
+ // appropriately.
+ coef = {b0 : 0, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ }
+ } else {
+ // When freq = 0 or 1, the z-transform is 1
+ coef = {b0 : 1, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ }
+
+ return coef;
+}
+
+function createAllpassFilter(freq, q, gain) {
+ var b0;
+ var b1;
+ var b2;
+ var a0;
+ var a1;
+ var a2;
+ var coef;
+
+ if (freq > 0 && freq < 1) {
+ if (q > 0) {
+ var w0 = Math.PI * freq;
+ var alpha = Math.sin(w0) / (2 * q);
+ var k = Math.cos(w0);
+
+ b0 = 1 - alpha;
+ b1 = -2 * k;
+ b2 = 1 + alpha;
+ a0 = 1 + alpha;
+ a1 = -2 * k;
+ a2 = 1 - alpha;
+ coef = normalizeFilterCoefficients(b0, b1, b2, a0, a1, a2);
+ } else {
+ // q = 0
+ coef = {b0 : -1, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ }
+ } else {
+ coef = {b0 : 1, b1 : 0, b2 : 0, a1 : 0, a2 : 0};
+ }
+
+ return coef;
+}
+
+function filterData(filterCoef, signal, len) {
+ var y = new Array(len);
+ var b0 = filterCoef.b0;
+ var b1 = filterCoef.b1;
+ var b2 = filterCoef.b2;
+ var a1 = filterCoef.a1;
+ var a2 = filterCoef.a2;
+
+ // Prime the pump. (Assumes the signal has length >= 2!)
+ y[0] = b0 * signal[0];
+ y[1] = b0 * signal[1] + b1 * signal[0] - a1 * y[0];
+
+ // Filter all of the signal that we have.
+ for (var k = 2; k < Math.min(signal.length, len); ++k) {
+ y[k] = b0 * signal[k] + b1 * signal[k-1] + b2 * signal[k-2] - a1 * y[k-1] - a2 * y[k-2];
+ }
+
+ // If we need to filter more, but don't have any signal left,
+ // assume the signal is zero.
+ for (var k = signal.length; k < len; ++k) {
+ y[k] = - a1 * y[k-1] - a2 * y[k-2];
+ }
+
+ return y;
+}
+
+// Map the filter type name to a function that computes the filter coefficents for the given filter
+// type.
+var filterCreatorFunction = {"lowpass": createLowpassFilter,
+ "highpass": createHighpassFilter,
+ "bandpass": createBandpassFilter,
+ "lowshelf": createLowShelfFilter,
+ "highshelf": createHighShelfFilter,
+ "peaking": createPeakingFilter,
+ "notch": createNotchFilter,
+ "allpass": createAllpassFilter};
+
+var filterTypeName = {"lowpass": "Lowpass filter",
+ "highpass": "Highpass filter",
+ "bandpass": "Bandpass filter",
+ "lowshelf": "Lowshelf filter",
+ "highshelf": "Highshelf filter",
+ "peaking": "Peaking filter",
+ "notch": "Notch filter",
+ "allpass": "Allpass filter"};
+
+function createFilter(filterType, freq, q, gain) {
+ return filterCreatorFunction[filterType](freq, q, gain);
+}new file mode 100644
--- /dev/null
+++ b/dom/media/webaudio/test/blink/iirfilter-getFrequencyResponse.html
@@ -0,0 +1,132 @@
+<!doctype html>
+<html>
+ <head>
+ <title>Test IIRFilter getFrequencyResponse() functionality</title>
+ <script src="../resources/js-test.js"></script>
+ <script src="resources/compatibility.js"></script>
+ <script src="resources/audio-testing.js"></script>
+ <script src="resources/biquad-filters.js"></script>
+ </head>
+
+ <body>
+ <script>
+ description("Test IIRFilter getFrequencyResponse() functionality");
+ window.jsTestIsAsync = true;
+
+ var sampleRate = 48000;
+ // Some short duration; we're not actually looking at the rendered output.
+ var testDurationSec = 0.01;
+
+ // Number of frequency samples to take.
+ var numberOfFrequencies = 1000;
+
+ var audit = Audit.createTaskRunner();
+
+
+ // Compute a set of linearly spaced frequencies.
+ function createFrequencies(nFrequencies, sampleRate)
+ {
+ var frequencies = new Float32Array(nFrequencies);
+ var nyquist = sampleRate / 2;
+ var freqDelta = nyquist / nFrequencies;
+
+ for (var k = 0; k < nFrequencies; ++k) {
+ frequencies[k] = k * freqDelta;
+ }
+
+ return frequencies;
+ }
+
+ audit.defineTask("1-pole IIR", function (done) {
+ var context = new OfflineAudioContext(1, testDurationSec * sampleRate, sampleRate);
+
+ var iir = context.createIIRFilter([1], [1, -0.9]);
+ var frequencies = createFrequencies(numberOfFrequencies, context.sampleRate);
+
+ var iirMag = new Float32Array(numberOfFrequencies);
+ var iirPhase = new Float32Array(numberOfFrequencies);
+ var trueMag = new Float32Array(numberOfFrequencies);
+ var truePhase = new Float32Array(numberOfFrequencies);
+
+ // The IIR filter is
+ // H(z) = 1/(1 - 0.9*z^(-1)).
+ //
+ // The frequency response is
+ // H(exp(j*w)) = 1/(1 - 0.9*exp(-j*w)).
+ //
+ // Thus, the magnitude is
+ // |H(exp(j*w))| = 1/sqrt(1.81-1.8*cos(w)).
+ //
+ // The phase is
+ // arg(H(exp(j*w)) = atan(0.9*sin(w)/(.9*cos(w)-1))
+
+ var frequencyScale = Math.PI / (sampleRate / 2);
+
+ for (var k = 0; k < frequencies.length; ++k) {
+ var omega = frequencyScale * frequencies[k];
+ trueMag[k] = 1/Math.sqrt(1.81-1.8*Math.cos(omega));
+ truePhase[k] = Math.atan(0.9 * Math.sin(omega) / (0.9 * Math.cos(omega) - 1));
+ }
+
+ iir.getFrequencyResponse(frequencies, iirMag, iirPhase);
+
+ var success = true;
+
+ // Thresholds were experimentally determined.
+ success = Should("1-pole IIR Magnitude Response", iirMag).beCloseToArray(trueMag, 2.8611e-6);
+ success = Should("1-pole IIR Phase Response", iirPhase).beCloseToArray(truePhase, 1.7882e-7)
+ && success;
+ if (success)
+ testPassed("1-pole IIR response matched expected response.\n");
+ else
+ testFailed("1-pole IIR response did not match expected response.\n");
+
+ done();
+ });
+
+ audit.defineTask("compare IIR and biquad", function(done) {
+ // Create an IIR filter equivalent to the biquad filter. Compute the frequency response for
+ // both and verify that they are the same.
+ var context = new OfflineAudioContext(1, testDurationSec * sampleRate, sampleRate);
+
+ var biquad = context.createBiquadFilter();
+ var coef = createFilter(biquad.type,
+ biquad.frequency.value / (context.sampleRate / 2),
+ biquad.Q.value,
+ biquad.gain.value);
+
+ var iir = context.createIIRFilter([coef.b0, coef.b1, coef.b2], [1, coef.a1, coef.a2]);
+
+ var frequencies = createFrequencies(numberOfFrequencies, context.sampleRate);
+ var biquadMag = new Float32Array(numberOfFrequencies);
+ var biquadPhase = new Float32Array(numberOfFrequencies);
+ var iirMag = new Float32Array(numberOfFrequencies);
+ var iirPhase = new Float32Array(numberOfFrequencies);
+
+ biquad.getFrequencyResponse(frequencies, biquadMag, biquadPhase);
+ iir.getFrequencyResponse(frequencies, iirMag, iirPhase);
+
+ var success = true;
+
+ // Thresholds were experimentally determined.
+ success = Should("IIR Magnitude Response", iirMag).beCloseToArray(biquadMag, 2.7419e-5);
+ success = Should("IIR Phase Response", iirPhase).beCloseToArray(biquadPhase, 2.7657e-5) && success;
+
+ if (success)
+ testPassed("IIR response matched equivalent " + biquad.type + " Biquad response.\n");
+ else
+ testFailed("IIR response did not equivalent " + biquad.type + " Biquad response.\n");
+
+ done();
+ });
+
+ audit.defineTask("finish", function (done) {
+ finishJSTest();
+ done();
+ });
+
+ audit.runTasks();
+ successfullyParsed = true;
+ </script>
+ </body>
+</html>new file mode 100644
--- /dev/null
+++ b/dom/media/webaudio/test/blink/iirfilter.html
@@ -0,0 +1,574 @@
+<!doctype html>
+<html>
+ <head>
+ <title>Test Basic IIRFilterNode Operation</title>
+ <script src="../resources/js-test.js"></script>
+ <script src="resources/compatibility.js"></script>
+ <script src="resources/audio-testing.js"></script>
+ <script src="resources/biquad-filters.js"></script>
+ </head>
+
+ <body>
+ <script>
+ description("Test Basic IIRFilterNode Operation");
+ window.jsTestIsAsync = true;
+
+ var sampleRate = 48000;
+ var testDurationSec = 1;
+ var testFrames = testDurationSec * sampleRate;
+
+ var audit = Audit.createTaskRunner();
+
+ audit.defineTask("coefficient-normalization", function (done) {
+ // Test that the feedback coefficients are normalized. Do this be creating two
+ // IIRFilterNodes. One has normalized coefficients, and one doesn't. Compute the
+ // difference and make sure they're the same.
+ var success = true;
+ var context = new OfflineAudioContext(2, testFrames, sampleRate);
+
+ // Use a simple impulse as the source.
+ var buffer = context.createBuffer(1, 1, sampleRate);
+ buffer.getChannelData(0)[0] = 1;
+ var source = context.createBufferSource();
+ source.buffer = buffer;
+
+ // Gain node for computing the difference between the filters.
+ var gain = context.createGain();
+ gain.gain.value = -1;
+
+ // The IIR filters. Use a common feedforward array.
+ var ff = [1];
+
+ var fb1 = [1, .9];
+
+ var fb2 = new Float64Array(2);
+ // Scale the feedback coefficients by an arbitrary factor.
+ var coefScaleFactor = 2;
+ for (var k = 0; k < fb2.length; ++k) {
+ fb2[k] = coefScaleFactor * fb1[k];
+ }
+
+ var iir1;
+ var iir2;
+
+ success = Should("createIIRFilter with normalized coefficients", function () {
+ iir1 = context.createIIRFilter(ff, fb1);
+ }).notThrow() && success;
+
+ success = Should("createIIRFilter with unnormalized coefficients", function () {
+ iir2 = context.createIIRFilter(ff, fb2);
+ }).notThrow() && success;
+
+ // Create the graph. The output of iir1 (normalized coefficients) is channel 0, and the
+ // output of iir2 (unnormalized coefficients), with appropriate scaling, is channel 1.
+ var merger = context.createChannelMerger(2);
+ source.connect(iir1);
+ source.connect(iir2);
+ iir1.connect(merger, 0, 0);
+ iir2.connect(gain);
+
+ // The gain for the gain node should be set to compensate for the scaling of the
+ // coefficients. Since iir2 has scaled the coefficients by coefScaleFactor, the output is
+ // reduced by the same factor, so adjust the gain to scale the output of iir2 back up.
+ gain.gain.value = coefScaleFactor;
+ gain.connect(merger, 0, 1);
+
+ merger.connect(context.destination);
+
+ source.start();
+
+ // Rock and roll!
+
+ context.startRendering().then(function (result) {
+ // Find the max amplitude of the result, which should be near zero.
+ var iir1Data = result.getChannelData(0);
+ var iir2Data = result.getChannelData(1);
+
+ // Threshold isn't exactly zero because the arithmetic is done differently between the
+ // IIRFilterNode and the BiquadFilterNode.
+ success = Should("Output of IIR filter with unnormalized coefficients", iir2Data)
+ .beCloseToArray(iir1Data, 2.1958e-38) && success;
+ if (success)
+ testPassed("IIRFilter coefficients correctly normalized.\n");
+ else
+ testFailed("IIRFilter coefficients not correctly normalized.\n");
+ }).then(done);
+ });
+
+ audit.defineTask("one-zero", function (done) {
+ // Create a simple 1-zero filter and compare with the expected output.
+ var context = new OfflineAudioContext(1, testFrames, sampleRate);
+
+ // Use a simple impulse as the source
+ var buffer = context.createBuffer(1, 1, sampleRate);
+ buffer.getChannelData(0)[0] = 1;
+ var source = context.createBufferSource();
+ source.buffer = buffer;
+
+ // The filter is y(n) = 0.5*(x(n) + x(n-1)), a simple 2-point moving average. This is
+ // rather arbitrary; keep it simple.
+
+ var iir = context.createIIRFilter([0.5, 0.5], [1]);
+
+ // Create the graph
+ source.connect(iir);
+ iir.connect(context.destination);
+
+ // Rock and roll!
+ source.start();
+
+ context.startRendering().then(function (result) {
+ var actual = result.getChannelData(0);
+ var expected = new Float64Array(testFrames);
+ // The filter is a simple 2-point moving average of an impulse, so the first two values
+ // are non-zero and the rest are zero.
+ expected[0] = 0.5;
+ expected[1] = 0.5;
+ Should('IIR 1-zero output', actual).beCloseToArray(expected, 0);
+ }).then(done);
+ });
+
+ audit.defineTask("one-pole", function (done) {
+ // Create a simple 1-pole filter and compare with the expected output.
+
+ // The filter is y(n) + c*y(n-1)= x(n). The analytical response is (-c)^n, so choose a
+ // suitable number of frames to run the test for where the output isn't flushed to zero.
+ var c = 0.9;
+ var eps = 1e-20;
+ var duration = Math.floor(Math.log(eps) / Math.log(Math.abs(c)));
+ var context = new OfflineAudioContext(1, duration, sampleRate);
+
+ // Use a simple impulse as the source
+ var buffer = context.createBuffer(1, 1, sampleRate);
+ buffer.getChannelData(0)[0] = 1;
+ var source = context.createBufferSource();
+ source.buffer = buffer;
+
+ var iir = context.createIIRFilter([1], [1, c]);
+
+ // Create the graph
+ source.connect(iir);
+ iir.connect(context.destination);
+
+ // Rock and roll!
+ source.start();
+
+ context.startRendering().then(function (result) {
+ var actual = result.getChannelData(0);
+ var expected = new Float64Array(actual.length);
+
+ // The filter is a simple 1-pole filter: y(n) = -c*y(n-k)+x(n), with an impulse as the
+ // input.
+ expected[0] = 1;
+ for (k = 1; k < testFrames; ++k) {
+ expected[k] = -c * expected[k-1];
+ }
+
+ // Threshold isn't exactly zero due to round-off in the single-precision IIRFilterNode
+ // computations versus the double-precision Javascript computations.
+ Should('IIR 1-pole output', actual, {verbose: true})
+ .beCloseToArray(expected, {relativeThreshold: 5.723e-8});
+ }).then(done);
+ });
+
+ // Return a function suitable for use as a defineTask function. This function creates an
+ // IIRFilterNode equivalent to the specified BiquadFilterNode and compares the outputs. The
+ // outputs from the two filters should be virtually identical.
+ function testWithBiquadFilter (filterType, errorThreshold, snrThreshold) {
+ return function (done) {
+ var context = new OfflineAudioContext(2, testFrames, sampleRate);
+
+ // Use a constant (step function) as the source
+ var buffer = createConstantBuffer(context, testFrames, 1);
+ var source = context.createBufferSource();
+ source.buffer = buffer;
+
+
+ // Create the biquad. Choose some rather arbitrary values for Q and gain for the biquad
+ // so that the shelf filters aren't identical.
+ var biquad = context.createBiquadFilter();
+ biquad.type = filterType;
+ biquad.Q.value = 10;
+ biquad.gain.value = 10;
+
+ // Create the equivalent IIR Filter node by computing the coefficients of the given biquad
+ // filter type.
+ var nyquist = sampleRate / 2;
+ var coef = createFilter(filterType,
+ biquad.frequency.value / nyquist,
+ biquad.Q.value,
+ biquad.gain.value);
+
+ var iir = context.createIIRFilter([coef.b0, coef.b1, coef.b2], [1, coef.a1, coef.a2]);
+
+ var merger = context.createChannelMerger(2);
+ // Create the graph
+ source.connect(biquad);
+ source.connect(iir);
+
+ biquad.connect(merger, 0, 0);
+ iir.connect(merger, 0, 1);
+
+ merger.connect(context.destination);
+
+ // Rock and roll!
+ source.start();
+
+ context.startRendering().then(function (result) {
+ // Find the max amplitude of the result, which should be near zero.
+ var expected = result.getChannelData(0);
+ var actual = result.getChannelData(1);
+
+ // On MacOSX, WebAudio uses an optimized Biquad implementation that is different from
+ // the implementation used for Linux and Windows. This will cause the output to differ,
+ // even if the threshold passes. Thus, only print out a very small number of elements
+ // of the array where we have tested that they are consistent.
+ Should("IIRFilter for Biquad " + filterType, actual, {
+ precision: 5,
+ verbose: true
+ })
+ .beCloseToArray(expected, errorThreshold);
+
+ var snr = 10*Math.log10(computeSNR(actual, expected));
+ Should("SNR for IIRFIlter for Biquad " + filterType, snr).beGreaterThanOrEqualTo(snrThreshold);
+ }).then(done);
+ };
+ }
+
+ // Thresholds here are experimentally determined.
+ var biquadTestConfigs = [{
+ filterType: "lowpass",
+ snrThreshold: 91.222,
+ errorThreshold: {
+ relativeThreshold: 4.15e-5
+ }
+ }, {
+ filterType: "highpass",
+ snrThreshold: 107.246,
+ errorThreshold: {
+ absoluteThreshold: 2.9e-6,
+ relativeThreshold: 3e-5
+ }
+ }, {
+ filterType: "bandpass",
+ snrThreshold: 104.060,
+ errorThreshold: {
+ absoluteThreshold: 2e-7,
+ relativeThreshold: 8.7e-4
+ }
+ }, {
+ filterType: "notch",
+ snrThreshold: 91.312,
+ errorThreshold: {
+ absoluteThreshold: 0,
+ relativeThreshold: 4.22e-5
+ }
+ }, {
+ filterType: "allpass",
+ snrThreshold: 91.319,
+ errorThreshold: {
+ absoluteThreshold: 0,
+ relativeThreshold: 4.31e-5
+ }
+ }, {
+ filterType: "lowshelf",
+ snrThreshold: 90.609,
+ errorThreshold: {
+ absoluteThreshold: 0,
+ relativeThreshold: 2.98e-5
+ }
+ }, {
+ filterType: "highshelf",
+ snrThreshold: 103.159,
+ errorThreshold: {
+ absoluteThreshold: 0,
+ relativeThreshold: 1.24e-5
+ }
+ }, {
+ filterType: "peaking",
+ snrThreshold: 91.504,
+ errorThreshold: {
+ absoluteThreshold: 0,
+ relativeThreshold: 5.05e-5
+ }
+ }];
+
+ // Create a set of tasks based on biquadTestConfigs.
+ for (k = 0; k < biquadTestConfigs.length; ++k) {
+ var config = biquadTestConfigs[k];
+ var name = k + ": " + config.filterType;
+ audit.defineTask(name, testWithBiquadFilter(config.filterType, config.errorThreshold, config.snrThreshold));
+ }
+
+ audit.defineTask("multi-channel", function (done) {
+ // Multi-channel test. Create a biquad filter and the equivalent IIR filter. Filter the
+ // same multichannel signal and compare the results.
+ var nChannels = 3;
+ var context = new OfflineAudioContext(nChannels, testFrames, sampleRate);
+
+ // Create a set of oscillators as the multi-channel source.
+ var source = [];
+
+ for (k = 0; k < nChannels; ++k) {
+ source[k] = context.createOscillator();
+ source[k].type = "sawtooth";
+ // The frequency of the oscillator is pretty arbitrary, but each oscillator should have a
+ // different frequency.
+ source[k].frequency.value = 100 + k * 100;
+ }
+
+ var merger = context.createChannelMerger(3);
+
+ var biquad = context.createBiquadFilter();
+
+ // Create the equivalent IIR Filter node.
+ var nyquist = sampleRate / 2;
+ var coef = createFilter(biquad.type,
+ biquad.frequency.value / nyquist,
+ biquad.Q.value,
+ biquad.gain.value);
+ var fb = [1, coef.a1, coef.a2];
+ var ff = [coef.b0, coef.b1, coef.b2];
+
+ var iir = context.createIIRFilter(ff, fb);
+ // Gain node to compute the difference between the IIR and biquad filter.
+ var gain = context.createGain();
+ gain.gain.value = -1;
+
+ // Create the graph.
+ for (k = 0; k < nChannels; ++k)
+ source[k].connect(merger, 0, k);
+
+ merger.connect(biquad);
+ merger.connect(iir);
+ iir.connect(gain);
+ biquad.connect(context.destination);
+ gain.connect(context.destination);
+
+ for (k = 0; k < nChannels; ++k)
+ source[k].start();
+
+ context.startRendering().then(function (result) {
+ var success = true;
+ var errorThresholds = [3.7671e-5, 3.0071e-5, 2.6241e-5];
+
+ // Check the difference signal on each channel
+ for (channel = 0; channel < result.numberOfChannels; ++channel) {
+ // Find the max amplitude of the result, which should be near zero.
+ var data = result.getChannelData(channel);
+ var maxError = data.reduce(function(reducedValue, currentValue) {
+ return Math.max(reducedValue, Math.abs(currentValue));
+ });
+
+ success = Should("Max difference between IIR and Biquad on channel " + channel,
+ maxError).beLessThanOrEqualTo(errorThresholds[channel]);
+ }
+
+ if (success) {
+ testPassed("IIRFilter correctly processed " + result.numberOfChannels +
+ "-channel input.");
+ } else {
+ testFailed("IIRFilter failed to correctly process " + result.numberOfChannels +
+ "-channel input.");
+ }
+ }).then(done);
+ });
+
+ // Apply an IIRFilter to the given input signal.
+ //
+ // IIR filter in the time domain is
+ //
+ // y[n] = sum(ff[k]*x[n-k], k, 0, M) - sum(fb[k]*y[n-k], k, 1, N)
+ //
+ function iirFilter(input, feedforward, feedback) {
+ // For simplicity, create an x buffer that contains the input, and a y buffer that contains
+ // the output. Both of these buffers have an initial work space to implement the initial
+ // memory of the filter.
+ var workSize = Math.max(feedforward.length, feedback.length);
+ var x = new Float32Array(input.length + workSize);
+
+ // Float64 because we want to match the implementation that uses doubles to minimize
+ // roundoff.
+ var y = new Float64Array(input.length + workSize);
+
+ // Copy the input over.
+ for (var k = 0; k < input.length; ++k)
+ x[k + feedforward.length] = input[k];
+
+ // Run the filter
+ for (var n = 0; n < input.length; ++n) {
+ var index = n + workSize;
+ var yn = 0;
+ for (var k = 0; k < feedforward.length; ++k)
+ yn += feedforward[k] * x[index - k];
+ for (var k = 0; k < feedback.length; ++k)
+ yn -= feedback[k] * y[index - k];
+
+ y[index] = yn;
+ }
+
+ return y.slice(workSize).map(Math.fround);
+ }
+
+ // Cascade the two given biquad filters to create one IIR filter.
+ function cascadeBiquads(f1Coef, f2Coef) {
+ // The biquad filters are:
+ //
+ // f1 = (b10 + b11/z + b12/z^2)/(1 + a11/z + a12/z^2);
+ // f2 = (b20 + b21/z + b22/z^2)/(1 + a21/z + a22/z^2);
+ //
+ // To cascade them, multiply the two transforms together to get a fourth order IIR filter.
+
+ var numProduct = [f1Coef.b0 * f2Coef.b0,
+ f1Coef.b0 * f2Coef.b1 + f1Coef.b1 * f2Coef.b0,
+ f1Coef.b0 * f2Coef.b2 + f1Coef.b1 * f2Coef.b1 + f1Coef.b2 * f2Coef.b0,
+ f1Coef.b1 * f2Coef.b2 + f1Coef.b2 * f2Coef.b1,
+ f1Coef.b2 * f2Coef.b2
+ ];
+
+ var denProduct = [1,
+ f2Coef.a1 + f1Coef.a1,
+ f2Coef.a2 + f1Coef.a1 * f2Coef.a1 + f1Coef.a2,
+ f1Coef.a1 * f2Coef.a2 + f1Coef.a2 * f2Coef.a1,
+ f1Coef.a2 * f2Coef.a2
+ ];
+
+ return {
+ ff: numProduct,
+ fb: denProduct
+ }
+ }
+
+ // Find the magnitude of the root of the quadratic that has the maximum magnitude.
+ //
+ // The quadratic is z^2 + a1 * z + a2 and we want the root z that has the largest magnitude.
+ function largestRootMagnitude(a1, a2) {
+ var discriminant = a1 * a1 - 4 * a2;
+ if (discriminant < 0) {
+ // Complex roots: -a1/2 +/- i*sqrt(-d)/2. Thus the magnitude of each root is the same
+ // and is sqrt(a1^2/4 + |d|/4)
+ var d = Math.sqrt(-discriminant);
+ return Math.hypot(a1 / 2, d / 2);
+ } else {
+ // Real roots
+ var d = Math.sqrt(discriminant);
+ return Math.max(Math.abs((-a1 + d) / 2), Math.abs((-a1 - d) / 2));
+ }
+ }
+
+ audit.defineTask("4th-order-iir", function(done) {
+ // Cascade 2 lowpass biquad filters and compare that with the equivalent 4th order IIR
+ // filter.
+
+ var nyquist = sampleRate / 2;
+ // Compute the coefficients of a lowpass filter.
+
+ // First some preliminary stuff. Compute the coefficients of the biquad. This is used to
+ // figure out how frames to use in the test.
+ var biquadType = "lowpass";
+ var biquadCutoff = 350;
+ var biquadQ = 5;
+ var biquadGain = 1;
+
+ var coef = createFilter(biquadType,
+ biquadCutoff / nyquist,
+ biquadQ,
+ biquadGain);
+
+ // Cascade the biquads together to create an equivalent IIR filter.
+ var cascade = cascadeBiquads(coef, coef);
+
+ // Since we're cascading two identical biquads, the root of denominator of the IIR filter is
+ // repeated, so the root of the denominator with the largest magnitude occurs twice. The
+ // impulse response of the IIR filter will be roughly c*(r*r)^n at time n, where r is the
+ // root of largest magnitude. This approximation gets better as n increases. We can use
+ // this to get a rough idea of when the response has died down to a small value.
+
+ // This is the value we will use to determine how many frames to render. Rendering too many
+ // is a waste of time and also makes it hard to compare the actual result to the expected
+ // because the magnitudes are so small that they could be mostly round-off noise.
+ //
+ // Find magnitude of the root with largest magnitude
+ var rootMagnitude = largestRootMagnitude(coef.a1, coef.a2);
+
+ // Find n such that |r|^(2*n) <= eps. That is, n = log(eps)/(2*log(r)). Somewhat
+ // arbitrarily choose eps = 1e-20;
+ var eps = 1e-20;
+ var framesForTest = Math.floor(Math.log(eps) / (2 * Math.log(rootMagnitude)));
+
+ // We're ready to create the graph for the test. The offline context has two channels:
+ // channel 0 is the expected (cascaded biquad) result and channel 1 is the actual IIR filter
+ // result.
+ var context = new OfflineAudioContext(2, framesForTest, sampleRate);
+
+ // Use a simple impulse with a large (arbitrary) amplitude as the source
+ var amplitude = 1;
+ var buffer = context.createBuffer(1, testFrames, sampleRate);
+ buffer.getChannelData(0)[0] = amplitude;
+ var source = context.createBufferSource();
+ source.buffer = buffer;
+
+ // Create the two biquad filters. Doesn't really matter what, but for simplicity we choose
+ // identical lowpass filters with the same parameters.
+ var biquad1 = context.createBiquadFilter();
+ biquad1.type = biquadType;
+ biquad1.frequency.value = biquadCutoff;
+ biquad1.Q.value = biquadQ;
+
+ var biquad2 = context.createBiquadFilter();
+ biquad2.type = biquadType;
+ biquad2.frequency.value = biquadCutoff;
+ biquad2.Q.value = biquadQ;
+
+ var iir = context.createIIRFilter(cascade.ff, cascade.fb);
+
+ // Create the merger to get the signals into multiple channels
+ var merger = context.createChannelMerger(2);
+
+ // Create the graph, filtering the source through two biquads.
+ source.connect(biquad1);
+ biquad1.connect(biquad2);
+ biquad2.connect(merger, 0, 0);
+
+ source.connect(iir);
+ iir.connect(merger, 0, 1);
+
+ merger.connect(context.destination);
+
+ // Now filter the source through the IIR filter.
+ var y = iirFilter(buffer.getChannelData(0), cascade.ff, cascade.fb);
+
+ // Rock and roll!
+ source.start();
+
+ context.startRendering().then(function(result) {
+ var expected = result.getChannelData(0);
+ var actual = result.getChannelData(1);
+
+ Should("4-th order IIRFilter (biquad ref)",
+ actual, {
+ verbose: true,
+ precision: 5
+ })
+ .beCloseToArray(expected, {
+ // Thresholds experimentally determined.
+ absoluteThreshold: 8.4e-8,
+ relativeThreshold: 5e-7,
+ });
+
+ var snr = 10*Math.log10(computeSNR(actual, expected));
+ Should("SNR of 4-th order IIRFilter (biquad ref)", snr)
+ .beGreaterThanOrEqualTo(110.684);
+ }).then(done);
+ });
+
+ audit.defineTask("finish", function (done) {
+ finishJSTest();
+ done();
+ });
+
+ audit.runTasks();
+ successfullyParsed = true;
+ </script>
+ </body>
+</html>