TTBandpassButterworth2.h

Go to the documentation of this file.

/** @file
 *
 * @ingroup dspFilterLib
 *
 * @brief #TTBandpassButterworth2 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/
 */


#ifndef __TT_BANDPASS_BUTTERWORTH_2_H__
#define __TT_BANDPASS_BUTTERWORTH_2_H__

#include "TTDSP.h"


/** 2nd order Butterworth bandpass filter; 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.
 */
class TTBandpassButterworth2 : public TTAudioObjectBase {
    TTCLASS_SETUP(TTBandpassButterworth2)

protected:

    TTFloat64           mFrequency;             ///< filter cutoff frequency
    TTFloat64           mQ;                     ///< filter resonance
    TTFloat64           mC, mD, mBw, mA0, mA2, mB1, mB2;    ///< filter coefficients. a1=0 and hence ignored
    TTSampleVector      mX1;                        ///< Input sample n-1
    TTSampleVector      mX2;                        ///< Input sample n-2
    TTSampleVector      mY1;                        ///< Output sample n-1
    TTSampleVector      mY2;                        ///< Output sample n-2

    /** Receives notifications when there are changes to the inherited 
        mMaxNumChannels attribute.  This allocates memory for xm1, xm2, ym1, and ym2 
        so that each channel's previous values are remembered.      */
    TTErr updateMaxNumChannels(const TTValue& oldMaxNumChannels, TTValue&);
    TTErr updateSampleRate(const TTValue& oldSampleRate, TTValue&);
    TTErr clear();
    
    void calculateCoefficients();
    
    /** Standard single value calculate method as used by DSP objects. */
    inline TTErr calculateValue(const TTFloat64& x, TTFloat64& y, TTPtrSizedInt channel);
    
    /** Standard audio processing method as used by TTBlue objects. */
    TTErr processAudio(TTAudioSignalArrayPtr inputs, TTAudioSignalArrayPtr outputs);
    
    /** Setter for the frequency attribute. */
    TTErr setFrequency(const TTValue& value);
    TTErr setQ(const TTValue& value);
    /** This algorithm uses an IIR filter, meaning that it relies on feedback.  If the filter should
     *  not be producing any signal (such as turning audio off and then back on in a host) or if the
     *  feedback has become corrupted (such as might happen if a NaN is fed in) then it may be 
     *  neccesary to clear the filter by calling this method.
     *  @return Returns a TTErr error code.                                             */
    
    
    /** Unit Tests
     @param returnedTestInfo        Used to return test information
     @return                        #TTErr error code if the method fails to execute, else #kTTErrNone.
     */
    virtual TTErr test(TTValue& returnedTestInfo);
};


#endif // __TT_BANDPASS_BUTTERWORTH_2_H__