TTAllpass4a.h

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/** @file
 *
 * @ingroup dspFilterLib
 *
 * @brief #TTAllpass4a is a fourth-order allpass filter.
 *
 * @details Essentially the same as #TTAllpass2a, but with some signs flipped.
 *  Based on Fredric J. Harris (2004): Multirate Signal Processing for Communication Systems, Prentice Hall, Chapter 10, Figure 42.
 *
 *
 * @authors Timothy Place, Trond Lossius
 *
 * @copyright Copyright © 2010, Timothy Place @n
 * This code is licensed under the terms of the "New BSD License" @n
 * http://creativecommons.org/licenses/BSD/
 */


#ifndef __TT_ALLPASS4A_H__
#define __TT_ALLPASS4A_H__

#include "TTDSP.h"


/** A second-order building-block allpass filter.
    Based on Multirate Signal Processing for Communication Systems, Chapter 10, Figure 42. 
 */
class TTAllpass4a : public TTAudioObjectBase {
    TTCLASS_SETUP(TTAllpass4a)

protected:

    TTFloat64           mD1;    ///< first coefficient
    TTFloat64           mD2;    ///< second coefficient
    TTFloat64           mD3;    ///< third coefficient
    TTFloat64           mD4;    ///< fourth coefficient

    TTSampleVector      mX1;    ///< previous input sample (n-1) for each channel
    TTSampleVector      mX2;    ///< previous input sample (n-2) for each channel
    TTSampleVector      mX3;    ///< previous input sample (n-3) for each channel
    TTSampleVector      mX4;    ///< previous input sample (n-4) for each channel
    TTSampleVector      mY1;    ///< previous output sample (n-1) for each channel
    TTSampleVector      mY2;    ///< previous output sample (n-2) for each channel
    TTSampleVector      mY3;    ///< previous output sample (n-3) for each channel
    TTSampleVector      mY4;    ///< previous output sample (n-4) for each channel
    
    // Notifications
    TTErr updateMaxNumChannels(const TTValue& oldMaxNumChannels, TTValue&);

    // Zero filter history
    TTErr clear();
    
    // Do the processing
    TTErr processAudio(TTAudioSignalArrayPtr inputs, TTAudioSignalArrayPtr outputs);
    
    /** 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);

public:
    TTErr calculateValue(const TTFloat64& x, TTFloat64& y, TTPtrSizedInt channel=0);
};


#endif // __TT_ALLPASS4A_H__