TTBandrejectButterworth2.cpp

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/** @file
 *
 * @ingroup dspFilterLib
 *
 * @brief #TTBandrejectButterworth2 is a second-order Butterworth bandpass filter.
 *
 * @details Butterworth filters have maximum flat frequency response in the pass band.
 *  Based on an algorithm from Dodge & Jerse (1997): Computer Music -
 *  Synthesis, Composition, and Performance. 2nd edition. Schirmer.
 *
 * @authors Trond Lossius, Timothy Place,
 *
 * @copyright Copyright © 2008, Trond Lossius @n
 * This code is licensed under the terms of the "New BSD License" @n
 * http://creativecommons.org/licenses/BSD/
 */


#include "TTBandrejectButterworth2.h"

#define thisTTClass         TTBandrejectButterworth2
#define thisTTClassName     "bandreject.butterworth.2"
#define thisTTClassTags     "dspFilterLib, audio, processor, filter, notch, butterworth"


TT_AUDIO_CONSTRUCTOR
{
    // register attributes
    addAttributeWithSetter(Frequency,   kTypeFloat64);
    addAttributeProperty(Frequency,         range,          TTValue(10.0, sr*0.45));
    addAttributeProperty(Frequency,         rangeChecking,  TT("clip"));

    addAttributeWithSetter(Q,           kTypeFloat64);

    // register for notifications from the parent class so we can allocate memory as required
    addUpdates(MaxNumChannels);
    // register for notifications from the parent class so we can recalculate coefficients as required
    addUpdates(SampleRate);
    // make the clear method available to the outside world
    addMessage(clear);

    // Set Defaults...
    setAttributeValue(kTTSym_maxNumChannels,    arguments);         // This attribute is inherited
    setAttributeValue(TT("frequency"),      1000.0);
    setAttributeValue(TT("q"),              50.0);
    setProcessMethod(processAudio);
    setCalculateMethod(calculateValue);

}


TTBandrejectButterworth2::~TTBandrejectButterworth2()
{
    ;
}


TTErr TTBandrejectButterworth2::updateMaxNumChannels(const TTValue& oldMaxNumChannels, TTValue&)
{
    mX1.resize(mMaxNumChannels);
    mX2.resize(mMaxNumChannels);
    mY1.resize(mMaxNumChannels);
    mY2.resize(mMaxNumChannels);
    clear();
    return kTTErrNone;
}


TTErr TTBandrejectButterworth2::updateSampleRate(const TTValue& oldSampleRate, TTValue&)
{
    TTValue v(mFrequency);
    return setFrequency(v);
}


TTErr TTBandrejectButterworth2::clear()
{
    mX1.assign(mMaxNumChannels, 0.0);
    mX2.assign(mMaxNumChannels, 0.0);
    mY1.assign(mMaxNumChannels, 0.0);
    mY2.assign(mMaxNumChannels, 0.0);
    return kTTErrNone;
}


TTErr TTBandrejectButterworth2::setFrequency(const TTValue& newValue)
{
    mFrequency = newValue;
    calculateCoefficients();
    return kTTErrNone;
}


TTErr TTBandrejectButterworth2::setQ(const TTValue& newValue)
{
    mQ = newValue;
    calculateCoefficients();
    return kTTErrNone;
}


void TTBandrejectButterworth2::calculateCoefficients()
{
    // Avoid dividing by zero
    if (mQ > 0.1)
        mBw = mFrequency/mQ;
    else
        mBw = mFrequency/0.1;
    mC = tan( kTTPi*(mBw/sr) );
    mD = cos( kTTTwoPi*(mFrequency/sr) );
    mA0 = 1.0 / (1.0 + mC);
    mA1 = -2.0 * mA0 * mD;
    //mA2 = mA0;
    //mB1 = mA1;
    mB2 = mA0 * (1.0 - mC);
}

inline TTErr TTBandrejectButterworth2::calculateValue(const TTFloat64& x, TTFloat64& y, TTPtrSizedInt channel)
{
    //y = TTAntiDenormal(mA0*x + mA1*mX1[channel] + mA2*mX2[channel] - mB1*mY1[channel] - mB2*mY2[channel]);
    // since mA0 = mA2 nd mB1 = mA1, one can optimize to:
     y = mA0*(x + mX2[channel]) + mA1*(mX1[channel] - mY1[channel]) - mB2*mY2[channel];
    TTZeroDenormal(y);
    mX2[channel] = mX1[channel];
    mX1[channel] = x;
    mY2[channel] = mY1[channel];
    mY1[channel] = y;
    return kTTErrNone;
}


TTErr TTBandrejectButterworth2::processAudio(TTAudioSignalArrayPtr inputs, TTAudioSignalArrayPtr outputs)
{
    TT_WRAP_CALCULATE_METHOD(calculateValue);
}