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//=============================================================================
// Zerberus
// Zample player
//
// Copyright (C) 2013 Werner Schweer
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License version 2
// as published by the Free Software Foundation and appearing in
// the file LICENCE.GPL
//=============================================================================
#ifndef __MFILTER_H__
#define __MFILTER_H__
struct Zone;
class Zerberus;
//---------------------------------------------------------
// Envelope
//---------------------------------------------------------
//Biquad filter implementation
class ZFilter {
public:
ZFilter();
void initialize(const Zerberus* zerberus, const Zone* z, int velocity);
void update();
float apply(float inputValue, bool leftChannel);
float interpolate(unsigned phase, short prevVal, short currVal, short nextVal, short nextNextVal) const; //pure function
private:
const Zerberus* zerberus;
const Zone* sampleZone;
float resonanceF = 0.f; // the resonance frequency in Hz
float last_resonanceF = 0.f; // current resonance frequency of the filter
// Serves as a flag: A deviation between fres and last_fres
// indicates, that the filter has to be recalculated.
float q_lin = 0.f; // the q-factor on a linear scale
float gain = 0.f; // Gain correction factor, depends on q
// Flag: If set, the filter will be set directly.
// Else it changes smoothly
bool firstRun = true;
struct FilterData {
float histX1 = 0.f;
float histX2 = 0.f;
float histY1 = 0.f;
float histY2 = 0.f;
};
FilterData monoL;
FilterData monoR;
// normalized filter coefficients (bX = bX/a0 and aX = aX/a0)
// see Robert Bristow-Johnson's 'Cookbook formulae for audio EQ biquad filter coefficients'
float b0 = 0.f; // b0 / a0
float b1 = 0.f; // b1 / a0
float b2 = 0.f; // b2 / a0
float a1 = 0.f; // a0 / a0
float a2 = 0.f; // a1 / a0
float b0_incr = 0.f;
float b1_incr = 0.f;
float b2_incr = 0.f;
float a1_incr = 0.f;
float a2_incr = 0.f;
int filter_coeff_incr_count = 0;
};
#endif //__MFILTER_H__
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