nanosynth/DiodeLadderFilter.cpp at master · essenbee/nanosynth · GitHub

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#include "DiodeLadderFilter.h"

CDiodeLadderFilter::CDiodeLadderFilter(void)
{
	// init
	m_dK = 0;
	m_dGamma = 0.0;

	// feedback scalars
	m_dSG1 = 0.0;
	m_dSG2 = 0.0;
	m_dSG3 = 0.0;
	m_dSG4 = 0.0;

	// set filter types
	m_LPF1.m_uFilterType = LPF1;
	m_LPF2.m_uFilterType = LPF1;
	m_LPF3.m_uFilterType = LPF1;
	m_LPF4.m_uFilterType = LPF1;

	// set default filter type
	m_uFilterType = LPF4;

	// flush everything
	reset();
}

CDiodeLadderFilter::~CDiodeLadderFilter(void)
{
}

void CDiodeLadderFilter::reset()
{
	// flush everything
	m_LPF1.reset();
	m_LPF2.reset();
	m_LPF3.reset();
	m_LPF4.reset();
}

// decode the Q value; Q on UI is 1->10
void CDiodeLadderFilter::setQControl(double dQControl)
{
	// this maps dQControl = 1->10 to K = 0 -> 17
	m_dK = (17.0)*(dQControl - 1.0)/(10.0 - 1.0);
}

void CDiodeLadderFilter::update()
{
	// base class does modulation
	CFilter::update();

	// calculate alphas
	double wd = 2*pi*m_dFc;
	double T  = 1/m_dSampleRate;
	double wa = (2/T)*tan(wd*T/2);
	double g = wa*T/2;

	// Big G's
	double G1, G2, G3, G4;

	G4 = 0.5*g/(1.0 + g);
	G3 = 0.5*g/(1.0 + g - 0.5*g*G4);
	G2 = 0.5*g/(1.0 + g - 0.5*g*G3);
	G1 = g/(1.0 + g - g*G2);

	m_dGamma = G4*G3*G2*G1;

	m_dSG1 =  G4*G3*G2;
	m_dSG2 =  G4*G3;
	m_dSG3 =  G4;
	m_dSG4 =  1.0;

	// set alphas
	double G = g/(1.0 + g);

	m_LPF1.m_dAlpha = G;
	m_LPF2.m_dAlpha = G;
	m_LPF3.m_dAlpha = G;
	m_LPF4.m_dAlpha = G;

	// set betas
	m_LPF1.m_dBeta = 1.0/(1.0 + g - g*G2);
	m_LPF2.m_dBeta = 1.0/(1.0 + g - 0.5*g*G3);
	m_LPF3.m_dBeta = 1.0/(1.0 + g - 0.5*g*G4);
	m_LPF4.m_dBeta = 1.0/(1.0 + g);

	// set deltas
	m_LPF1.m_dDelta = g;
	m_LPF2.m_dDelta = 0.5*g;
	m_LPF3.m_dDelta = 0.5*g;
	m_LPF4.m_dDelta = 0.0;

	m_LPF1.m_dGamma = 1.0 + G1*G2;
	m_LPF2.m_dGamma = 1.0 + G2*G3;
	m_LPF3.m_dGamma = 1.0 + G3*G4;
	m_LPF4.m_dGamma = 1.0;

	// set epsilons
	m_LPF1.m_dEpsilon = G2;
	m_LPF2.m_dEpsilon = G3;
	m_LPF3.m_dEpsilon = G4;
	m_LPF4.m_dEpsilon = 0.0;

	// set a0s
	m_LPF1.m_da0 = 1.0;
	m_LPF2.m_da0 = 0.5;
	m_LPF3.m_da0 = 0.5;
	m_LPF4.m_da0 = 0.5;
}