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 /*

  * Copyright (C) 2010 Google Inc. All rights reserved.

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  * modification, are permitted provided that the following conditions

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  *     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

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 #ifndef Biquad_h

 #define Biquad_h

 #include <complex>

 namespace WebCore {

 typedef std::complex<double> Complex;

 // A basic biquad (two-zero / two-pole digital filter)

 //

 // It can be configured to a number of common and very useful filters:

 //    lowpass, highpass, shelving, parameteric, notch, allpass, ...

 class Biquad {

 public:

     Biquad();

     ~Biquad();

     void process(const float* sourceP, float* destP, size_t framesToProcess);

     // frequency is 0 - 1 normalized, resonance and dbGain are in decibels.

     // Q is a unitless quality factor.

     void setLowpassParams(double frequency, double resonance);

     void setHighpassParams(double frequency, double resonance);

     void setBandpassParams(double frequency, double Q);

     void setLowShelfParams(double frequency, double dbGain);

     void setHighShelfParams(double frequency, double dbGain);

     void setPeakingParams(double frequency, double Q, double dbGain);

     void setAllpassParams(double frequency, double Q);

     void setNotchParams(double frequency, double Q);

     // Set the biquad coefficients given a single zero (other zero will be conjugate)

     // and a single pole (other pole will be conjugate)

     void setZeroPolePairs(const Complex& zero, const Complex& pole);

     // Set the biquad coefficients given a single pole (other pole will be conjugate)

     // (The zeroes will be the inverse of the poles)

     void setAllpassPole(const Complex& pole);

     // Return true iff the next output block will contain sound even with

     // silent input.

     bool hasTail() const { return m_y1 || m_y2 || m_x1 || m_x2; }

     // Resets filter state

     void reset();

     // Filter response at a set of n frequencies. The magnitude and

     // phase response are returned in magResponse and phaseResponse.

     // The phase response is in radians.

     void getFrequencyResponse(int nFrequencies,

                               const float* frequency,

                               float* magResponse,

                               float* phaseResponse);

 private:

     void setNormalizedCoefficients(double b0, double b1, double b2, double a0, double a1, double a2);

     // Filter coefficients. The filter is defined as

     //

     // y[n] + m_a1*y[n-1] + m_a2*y[n-2] = m_b0*x[n] + m_b1*x[n-1] + m_b2*x[n-2].

     double m_b0;

     double m_b1;

     double m_b2;

     double m_a1;

     double m_a2;

     // Filter memory

     //

     // Double precision for the output values is valuable because errors can

     // accumulate.  Input values are also stored as double so they need not be

     // converted again for computation.

     double m_x1; // input delayed by 1 sample

     double m_x2; // input delayed by 2 samples

     double m_y1; // output delayed by 1 sample

     double m_y2; // output delayed by 2 samples

 };

 } // namespace WebCore

 #endif // Biquad_h