Implement IIRFilter node for WebAudio.

third_party/WebKit/LayoutTests/webaudio/resources/biquad-testing.js

 // Globals, to make testing and debugging easier.
 var context;
 var filter;
 var signal;
 var renderedBuffer;
 var renderedData;
 
 var sampleRate = 44100.0;
 var pulseLengthFrames = .1 * sampleRate;
 
@@ skipping 10 matching lines @@
 
 // How long to render.  Must be long enough for all of the filters we
 // want to test.
 var renderLengthSeconds = timeStep * (maxFilters + 1) ;
 
 var renderLengthSamples = Math.round(renderLengthSeconds * sampleRate);
 
 // Number of filters that will be processed.
 var nFilters;
 
-// 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;
-}
-
-// 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);
-}
-
 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];
@@ skipping 155 matching lines @@
         }
         
         if (success) {
             testPassed("Test signal was correctly filtered.");
         } else {
             testFailed("Test signal was not correctly filtered.");
         }
         finishJSTest();
     }
 }