/*
* Copyright (C) 2010 Google Inc. All rights reserved.
*
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* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of Apple Computer, Inc. ("Apple") nor the names of
* its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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*/
#include "Biquad.h"
#include "DenormalDisabler.h"
#include <
float.h>
#include <algorithm>
#include <math.h>
#include "fdlibm.h"
namespace WebCore {
Biquad::Biquad() {
// Initialize as pass-thru (straight-wire, no filter effect)
setNormalizedCoefficients(1, 0, 0, 1, 0, 0);
reset();
// clear filter memory
}
Biquad::~Biquad() =
default;
void Biquad::process(
const float* sourceP,
float* destP,
size_t framesToProcess) {
// Create local copies of member variables
double x1 = m_x1;
double x2 = m_x2;
double y1 = m_y1;
double y2 = m_y2;
double b0 = m_b0;
double b1 = m_b1;
double b2 = m_b2;
double a1 = m_a1;
double a2 = m_a2;
for (size_t i = 0; i < framesToProcess; ++i) {
// FIXME: this can be optimized by pipelining the multiply adds...
double x = sourceP[i];
double y = b0 * x + b1 * x1 + b2 * x2 - a1 * y1 - a2 * y2;
destP[i] = y;
// Update state variables
x2 = x1;
x1 = x;
y2 = y1;
y1 = y;
}
// Avoid introducing a stream of subnormals when input is silent and the
// tail approaches zero.
if (x1 == 0.0 && x2 == 0.0 && (y1 != 0.0 || y2 != 0.0) &&
fabs(y1) < FLT_MIN && fabs(y2) < FLT_MIN) {
// Flush future values to zero (until there is new input).
y1 = y2 = 0.0;
// Flush calculated values.
#ifndef HAVE_DENORMAL
for (
int i = framesToProcess; i-- && fabsf(destP[i]) < FLT_MIN;) {
destP[i] = 0.0f;
}
#endif
}
// Local variables back to member.
m_x1 = x1;
m_x2 = x2;
m_y1 = y1;
m_y2 = y2;
}
void Biquad::reset() { m_x1 = m_x2 = m_y1 = m_y2 = 0; }
void Biquad::setLowpassParams(
double cutoff,
double resonance) {
// Limit cutoff to 0 to 1.
cutoff = std::max(0.0, std::min(cutoff, 1.0));
if (cutoff == 1) {
// When cutoff is 1, the z-transform is 1.
setNormalizedCoefficients(1, 0, 0, 1, 0, 0);
}
else if (cutoff > 0) {
// Compute biquad coefficients for lowpass filter
double g = fdlibm_pow(10.0, -0.05 * resonance);
double w0 = M_PI * cutoff;
double cos_w0 = fdlibm_cos(w0);
double alpha = 0.5 * fdlibm_sin(w0) * g;
double b1 = 1.0 - cos_w0;
double b0 = 0.5 * b1;
double b2 = b0;
double a0 = 1.0 + alpha;
double a1 = -2.0 * cos_w0;
double a2 = 1.0 - alpha;
setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
}
else {
// When cutoff is zero, nothing gets through the filter, so set
// coefficients up correctly.
setNormalizedCoefficients(0, 0, 0, 1, 0, 0);
}
}
void Biquad::setHighpassParams(
double cutoff,
double resonance) {
// Limit cutoff to 0 to 1.
cutoff = std::max(0.0, std::min(cutoff, 1.0));
if (cutoff == 1) {
// The z-transform is 0.
setNormalizedCoefficients(0, 0, 0, 1, 0, 0);
}
else if (cutoff > 0) {
// Compute biquad coefficients for highpass filter
double g = fdlibm_pow(10.0, -0.05 * resonance);
double w0 = M_PI * cutoff;
double cos_w0 = fdlibm_cos(w0);
double alpha = 0.5 * fdlibm_sin(w0) * g;
double b1 = -1.0 - cos_w0;
double b0 = -0.5 * b1;
double b2 = b0;
double a0 = 1.0 + alpha;
double a1 = -2.0 * cos_w0;
double a2 = 1.0 - alpha;
setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
}
else {
// When cutoff is zero, we need to be careful because the above
// gives a quadratic divided by the same quadratic, with poles
// and zeros on the unit circle in the same place. When cutoff
// is zero, the z-transform is 1.
setNormalizedCoefficients(1, 0, 0, 1, 0, 0);
}
}
void Biquad::setNormalizedCoefficients(
double b0,
double b1,
double b2,
double a0,
double a1,
double a2) {
double a0Inverse = 1 / a0;
m_b0 = b0 * a0Inverse;
m_b1 = b1 * a0Inverse;
m_b2 = b2 * a0Inverse;
m_a1 = a1 * a0Inverse;
m_a2 = a2 * a0Inverse;
}
void Biquad::setLowShelfParams(
double frequency,
double dbGain) {
// Clip frequencies to between 0 and 1, inclusive.
frequency = std::max(0.0, std::min(frequency, 1.0));
double A = fdlibm_pow(10.0, dbGain / 40);
if (frequency == 1) {
// The z-transform is a constant gain.
setNormalizedCoefficients(A * A, 0, 0, 1, 0, 0);
}
else if (frequency > 0) {
double w0 = M_PI * frequency;
double S = 1;
// filter slope (1 is max value)
double alpha = 0.5 * fdlibm_sin(w0) * sqrt((A + 1 / A) * (1 / S - 1) + 2);
double k = fdlibm_cos(w0);
double k2 = 2 * sqrt(A) * alpha;
double aPlusOne = A + 1;
double aMinusOne = A - 1;
double b0 = A * (aPlusOne - aMinusOne * k + k2);
double b1 = 2 * A * (aMinusOne - aPlusOne * k);
double b2 = A * (aPlusOne - aMinusOne * k - k2);
double a0 = aPlusOne + aMinusOne * k + k2;
double a1 = -2 * (aMinusOne + aPlusOne * k);
double a2 = aPlusOne + aMinusOne * k - k2;
setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
}
else {
// When frequency is 0, the z-transform is 1.
setNormalizedCoefficients(1, 0, 0, 1, 0, 0);
}
}
void Biquad::setHighShelfParams(
double frequency,
double dbGain) {
// Clip frequencies to between 0 and 1, inclusive.
frequency = std::max(0.0, std::min(frequency, 1.0));
double A = fdlibm_pow(10.0, dbGain / 40);
if (frequency == 1) {
// The z-transform is 1.
setNormalizedCoefficients(1, 0, 0, 1, 0, 0);
}
else if (frequency > 0) {
double w0 = M_PI * frequency;
double S = 1;
// filter slope (1 is max value)
double alpha = 0.5 * fdlibm_sin(w0) * sqrt((A + 1 / A) * (1 / S - 1) + 2);
double k = fdlibm_cos(w0);
double k2 = 2 * sqrt(A) * alpha;
double aPlusOne = A + 1;
double aMinusOne = A - 1;
double b0 = A * (aPlusOne + aMinusOne * k + k2);
double b1 = -2 * A * (aMinusOne + aPlusOne * k);
double b2 = A * (aPlusOne + aMinusOne * k - k2);
double a0 = aPlusOne - aMinusOne * k + k2;
double a1 = 2 * (aMinusOne - aPlusOne * k);
double a2 = aPlusOne - aMinusOne * k - k2;
setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
}
else {
// When frequency = 0, the filter is just a gain, A^2.
setNormalizedCoefficients(A * A, 0, 0, 1, 0, 0);
}
}
void Biquad::setPeakingParams(
double frequency,
double Q,
double dbGain) {
// Clip frequencies to between 0 and 1, inclusive.
frequency = std::max(0.0, std::min(frequency, 1.0));
// Don't let Q go negative, which causes an unstable filter.
Q = std::max(0.0, Q);
double A = fdlibm_pow(10.0, dbGain / 40);
if (frequency > 0 && frequency < 1) {
if (Q > 0) {
double w0 = M_PI * frequency;
double alpha = fdlibm_sin(w0) / (2 * Q);
double k = fdlibm_cos(w0);
double b0 = 1 + alpha * A;
double b1 = -2 * k;
double b2 = 1 - alpha * A;
double a0 = 1 + alpha / A;
double a1 = -2 * k;
double a2 = 1 - alpha / A;
setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
}
else {
// When Q = 0, the above formulas have problems. If we look at
// the z-transform, we can see that the limit as Q->0 is A^2, so
// set the filter that way.
setNormalizedCoefficients(A * A, 0, 0, 1, 0, 0);
}
}
else {
// When frequency is 0 or 1, the z-transform is 1.
setNormalizedCoefficients(1, 0, 0, 1, 0, 0);
}
}
void Biquad::setAllpassParams(
double frequency,
double Q) {
// Clip frequencies to between 0 and 1, inclusive.
frequency = std::max(0.0, std::min(frequency, 1.0));
// Don't let Q go negative, which causes an unstable filter.
Q = std::max(0.0, Q);
if (frequency > 0 && frequency < 1) {
if (Q > 0) {
double w0 = M_PI * frequency;
double alpha = fdlibm_sin(w0) / (2 * Q);
double k = fdlibm_cos(w0);
double b0 = 1 - alpha;
double b1 = -2 * k;
double b2 = 1 + alpha;
double a0 = 1 + alpha;
double a1 = -2 * k;
double a2 = 1 - alpha;
setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
}
else {
// When Q = 0, the above formulas have problems. If we look at
// the z-transform, we can see that the limit as Q->0 is -1, so
// set the filter that way.
setNormalizedCoefficients(-1, 0, 0, 1, 0, 0);
}
}
else {
// When frequency is 0 or 1, the z-transform is 1.
setNormalizedCoefficients(1, 0, 0, 1, 0, 0);
}
}
void Biquad::setNotchParams(
double frequency,
double Q) {
// Clip frequencies to between 0 and 1, inclusive.
frequency = std::max(0.0, std::min(frequency, 1.0));
// Don't let Q go negative, which causes an unstable filter.
Q = std::max(0.0, Q);
if (frequency > 0 && frequency < 1) {
if (Q > 0) {
double w0 = M_PI * frequency;
double alpha = fdlibm_sin(w0) / (2 * Q);
double k = fdlibm_cos(w0);
double b0 = 1;
double b1 = -2 * k;
double b2 = 1;
double a0 = 1 + alpha;
double a1 = -2 * k;
double a2 = 1 - alpha;
setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
}
else {
// When Q = 0, the above formulas have problems. If we look at
// the z-transform, we can see that the limit as Q->0 is 0, so
// set the filter that way.
setNormalizedCoefficients(0, 0, 0, 1, 0, 0);
}
}
else {
// When frequency is 0 or 1, the z-transform is 1.
setNormalizedCoefficients(1, 0, 0, 1, 0, 0);
}
}
void Biquad::setBandpassParams(
double frequency,
double Q) {
// No negative frequencies allowed.
frequency = std::max(0.0, frequency);
// Don't let Q go negative, which causes an unstable filter.
Q = std::max(0.0, Q);
if (frequency > 0 && frequency < 1) {
double w0 = M_PI * frequency;
if (Q > 0) {
double alpha = fdlibm_sin(w0) / (2 * Q);
double k = fdlibm_cos(w0);
double b0 = alpha;
double b1 = 0;
double b2 = -alpha;
double a0 = 1 + alpha;
double a1 = -2 * k;
double a2 = 1 - alpha;
setNormalizedCoefficients(b0, b1, b2, a0, a1, a2);
}
else {
// When Q = 0, the above formulas have problems. If we look at
// the z-transform, we can see that the limit as Q->0 is 1, so
// set the filter that way.
setNormalizedCoefficients(1, 0, 0, 1, 0, 0);
}
}
else {
// When the cutoff is zero, the z-transform approaches 0, if Q
// > 0. When both Q and cutoff are zero, the z-transform is
// pretty much undefined. What should we do in this case?
// For now, just make the filter 0. When the cutoff is 1, the
// z-transform also approaches 0.
setNormalizedCoefficients(0, 0, 0, 1, 0, 0);
}
}
void Biquad::setZeroPolePairs(
const Complex& zero,
const Complex& pole) {
double b0 = 1;
double b1 = -2 * zero.real();
double zeroMag = abs(zero);
double b2 = zeroMag * zeroMag;
double a1 = -2 * pole.real();
double poleMag = abs(pole);
double a2 = poleMag * poleMag;
setNormalizedCoefficients(b0, b1, b2, 1, a1, a2);
}
void Biquad::setAllpassPole(
const Complex& pole) {
Complex zero = Complex(1, 0) / pole;
setZeroPolePairs(zero, pole);
}
void Biquad::getFrequencyResponse(
int nFrequencies,
const float* frequency,
float* magResponse,
float* phaseResponse) {
// Evaluate the Z-transform of the filter at given normalized
// frequency from 0 to 1. (1 corresponds to the Nyquist
// frequency.)
//
// The z-transform of the filter is
//
// H(z) = (b0 + b1*z^(-1) + b2*z^(-2))/(1 + a1*z^(-1) + a2*z^(-2))
//
// Evaluate as
//
// b0 + (b1 + b2*z1)*z1
// --------------------
// 1 + (a1 + a2*z1)*z1
//
// with z1 = 1/z and z = exp(j*pi*frequency). Hence z1 = exp(-j*pi*frequency)
// Make local copies of the coefficients as a micro-optimization.
double b0 = m_b0;
double b1 = m_b1;
double b2 = m_b2;
double a1 = m_a1;
double a2 = m_a2;
for (
int k = 0; k < nFrequencies; ++k) {
double omega = -M_PI * frequency[k];
Complex z = Complex(fdlibm_cos(omega), fdlibm_sin(omega));
Complex numerator = b0 + (b1 + b2 * z) * z;
Complex denominator = Complex(1, 0) + (a1 + a2 * z) * z;
// Strangely enough, using complex division:
// e.g. Complex response = numerator / denominator;
// fails on our test machines, yielding infinities and NaNs, so we do
// things the long way here.
double n = norm(denominator);
double r = (real(numerator) * real(denominator) +
imag(numerator) * imag(denominator)) /
n;
double i = (imag(numerator) * real(denominator) -
real(numerator) * imag(denominator)) /
n;
std::complex<
double> response = std::complex<
double>(r, i);
magResponse[k] =
static_cast<
float>(fdlibm_hypot(real(response), imag(response)));
phaseResponse[k] =
static_cast<
float>(fdlibm_atan2(imag(response), real(response)));
}
}
}
// namespace WebCore
