Filters.h

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///
/// Filters.h -- CSL filter classes.
/// 
/// The base Filter class can perform the generic filter equation based upon a set of feedback 
/// and feedforward coefficients. Subclasses of Filter implement the setupCoeffs method to build 
/// these coefficients according to different algorithms.
/// The subclasses here mostly inherit from the FrequencyAmount controllable, which specifies a 
/// center frequency and an 'amount' which may variously be resonance, radius, bandwidth etc 
/// according to the algorithm.
/// 
/// OK so for example Butter class has a CenterFrequency port and a Bandwidth port,
/// but pull_controls must be calling Controllables to do the pullInput()
/// 
/// Or, a generic filter that can take a multichannel UGen for each of aCoeffs and bCoeffs (i.e. 
/// multichannel ports), and other filter classes that wrap this and have Frequency and Bandwidth ports etc.
/// This reduces the calls to setupCoeffs, because they'd actually be part of the nextBuffer instead
/// 
/// The reason is that the Scalable type approach & macros can't be extended to filter otherwise.
/// ALSO, there are no similar macros for Effect; how should this work?
/// 
/// OK, the way he had it working here is filtering in place, i.e. no internal buffer, 
/// but if I inherit from Effect, I do have an internal buffer; this means the first thing to do is 
/// memcopy the input to the output, then pounce on that; or do the in-place stuff in the Effect port 
/// and finally copy to output, say with scale & offset performed there.
/// 
/// See the copyright notice and acknowledgment of authors in the file COPYRIGHT
///

#ifndef CSL_Filters_H
#define CSL_Filters_H

#define FILTER_MAX_COEFFICIENTS (16)            // seems reasonable?

#include "CSL_Core.h"

namespace csl {

#ifdef CSL_ENUMS

typedef enum {
    BW_LOW_PASS = 0,
    BW_HIGH_PASS,
    BW_BAND_PASS,
    BW_BAND_STOP
} ButterworthType;
#else
    #define BW_LOW_PASS 0
    #define BW_HIGH_PASS 1
    #define BW_BAND_PASS 2
    #define BW_BAND_STOP 3
    typedef int ButterworthType;
#endif

/// Declare the pointer to freq/bw buffers (if used) and current scale/offset values

#define DECLARE_FILTER_CONTROLS                                     \
    Port * freqPort = mInputs[CSL_FILTER_FREQUENCY];                \
    Port * bwPort = mInputs[CSL_FILTER_AMOUNT]

/// Load the freq/bw-related values at the start

#define LOAD_FILTER_CONTROLS                                        \
    if (freqPort) Controllable::pullInput(freqPort, numFrames);     \
    if (bwPort) Controllable::pullInput(bwPort, numFrames)

/// FrequencyAmount -- mix-in class with frequency and amount (BW) control inputs (may be constants or
/// generators). amount (probably 0..1) is a generalised placeholder for bandwidth, resonance or radius, 
/// according to filter type or could equally be used as a kind of x,y location in the frequency domain

class FrequencyAmount : public virtual Controllable {
public:     
    FrequencyAmount();                              ///< Constructors
/*  FrequencyAmount(float frequency, float amount = 1.f);       ///< also specify bandwidth/radius/resonance etc.
    FrequencyAmount(UnitGenerator & frequency, float amount = 1.f); 
    FrequencyAmount(UnitGenerator & frequency, UnitGenerator & amount);
*/  ~FrequencyAmount();                             ///< Destructor
    
                                                    // accessors
    void setFrequency(UnitGenerator & frequency);   ///< set the receiver's frequency to a UGen or a float
    void setFrequency(float frequency);
    float getFrequency();

    void setAmount(UnitGenerator & amount);         ///< set the receiver's amount to a UGen or a float
    void setAmount(float amount);
};

///
/// Filter: the canonical-form n-pole/m-zero filter class
///

class Filter : public Effect, public Scalable, public FrequencyAmount {
    
public:
    Filter();
    Filter(unsigned num_b, unsigned num_a = 1);
    Filter(UnitGenerator & in, unsigned num_b = 1, unsigned num_a = 1);
    Filter(UnitGenerator & in, SampleBuffer bCoeffs, SampleBuffer aCoeffs, unsigned num_b, unsigned num_a);
    ~Filter();

    void clear(void);                               ///< clears the input/output buffers
    virtual void setupCoeffs() { };                 ///< to be overloaded by subclasses
                                                    /// supply the coefficients directly
    void setupCoeffs(SampleBuffer bCoeffs, SampleBuffer aCoeffs, unsigned num_b, unsigned num_a );
    
    virtual void nextBuffer(Buffer & outputBuffer, unsigned outBufNum) throw (CException);
    
    void dump();                                    ///< log information about myself
    
protected:
    void init(unsigned a, unsigned b);              ///< shared initialization function

    float mBCoeff[FILTER_MAX_COEFFICIENTS];         ///< array of numerator coeffs
    float mACoeff[FILTER_MAX_COEFFICIENTS];         ///< array of denominator coeffs
    unsigned mBNum;                                 ///< number of coeffs in b
    unsigned mANum;                                 ///< number of coeffs in a
    Buffer * mPrevInputs;                           ///< arrays of past input and output samples
    Buffer * mPrevOutputs;
    float mFrame;                                   ///< to keep hold of sample rate for calculating coeffs
};

/// Butterworth IIR (2nd order recursive) filter.
/// This operates upon a buffer of frames of amplitude samples by applying the following equation
/// y(n) = a0*x(n) + a1*x(n-1) + a2*x(n-2) - b1*y(n-1) - b2*y(n-2) where x is an amplitude sample.
/// It has constructors that can calculate the coefficients from a given cutoff frequency.

class Butter : public Filter {
    
public:
                // constructors / destructor
    Butter ();
    Butter (ButterworthType type, float cutoff);
    Butter (ButterworthType type, float center, float bandwidth);
    Butter (UnitGenerator & in, ButterworthType type, float cutoff);
    Butter (UnitGenerator & in, ButterworthType type, UnitGenerator & cutoff);
    Butter (UnitGenerator & in, ButterworthType type, float center, float bandwidth);
    Butter (UnitGenerator & in, ButterworthType type, UnitGenerator & center, UnitGenerator & bandwidth);
                // Filtering
    void setupCoeffs ();

protected:
    int mFilterType;                // flag as to what kind of filter I am

};

/// Formant Filter with zeros at +-z and complex conjugate poles at +-omega.
/// setupCoeffs() looks at the member var called normalize;
/// if normalize is true, the filter zeros are placed at z = 1, z = -1, and the coefficients 
/// are then normalized to produce a constant unity peak gain. The resulting filter 
/// frequency response has a resonance at the given frequency. The closer the poles 
/// are to the unit-circle (radius close to one), the narrower the resulting resonance width.

class Formant : public Filter {
    
public:
                /// constructors & destructor
    Formant (UnitGenerator & in, float center_freq, float radius);
    Formant (UnitGenerator & in, UnitGenerator & center_freq, float radius);
    ~Formant(void) { };
    
                /// Filtering methods
    void setupCoeffs();
    void setNormalize(bool normalize);

protected:
    bool                mNormalize;
};

/// Notch Filter with poles at +-z and complex conjugate zeros at +-omega.

class Notch : public Filter {
    
public:
                /// constructors & destructor
    Notch (UnitGenerator & in, float center_freq, float radius);
    Notch (UnitGenerator & in, UnitGenerator & center_freq, float radius);
    ~Notch(void) { };
                // Filtering
    void setupCoeffs ();

};

/// Allpass Filter with a pole and a zero at equal frequency and straddling the unit circle.
/// Allows all freqs to pass through but messes with phases.
/// Note that the Amount parameter of FrequencyAmount is ignored.

class Allpass : public Filter {

public:
                // constructors / destructor
    Allpass (UnitGenerator & in, float coeff);
    Allpass (UnitGenerator & in, UnitGenerator & coeff);
    ~Allpass(void) { };
                // Filtering
    void setupCoeffs();
    
protected:
    UnitGenerator *     mCoeffUGen;
    float               mCoeff;
    Buffer              mCoeffBuffer;
};

/// Moog VCF class

class Moog : public Filter {

public:
                // constructors / destructor
    Moog (UnitGenerator & in);
    Moog (UnitGenerator & in, UnitGenerator & cutoff);
    Moog (UnitGenerator & in, UnitGenerator & cutoff, UnitGenerator & resonance);
    Moog (UnitGenerator & in, float cutoff);
    Moog (UnitGenerator & in, float cutoff, float resonance);
    ~Moog (void) { };
                // Filtering
    void setupCoeffs ();
    
    void nextBuffer(Buffer & outputBuffer, unsigned outBufNum) throw (CException);  

protected:
    float               k, p, r;    // coefficients
    float               x, oldx;
    float               y1, y2, y3, y4, oldy1, oldy2, oldy3;
    bool                debugging;
};

}

#endif