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#ifndef __IIRfilter
#include "IIRfilter.h"
#endif
#include <math.h>
//------------------------------------------------------------------------
IIRfilter::IIRfilter()
{
reset();
}
//------------------------------------------------------------------------
IIRfilter::~IIRfilter() { }
//------------------------------------------------------------------------
void IIRfilter::calculateLowpassCoefficients(float cutoff, float samplerate)
{
float twoPiFreqDivSR, cosTwoPiFreqDivSR, Q, slopeFactor, coeffScalar;
Q = 0.5f;
twoPiFreqDivSR = 2.0f * PI * cutoff / samplerate; // ¹ ... 0
cosTwoPiFreqDivSR = cosf(twoPiFreqDivSR); // 1 ... -1
slopeFactor = sinf(twoPiFreqDivSR) / (Q * 2.0f); // 0 ... 1 ... 0
coeffScalar = 1.0f / (1.0f + slopeFactor); // 1 ... 0.5 ... 1
// calculate filter coefficients
pInCoeff = (1.0f - cosTwoPiFreqDivSR) * coeffScalar; // 0 ... 2
inCoeff = ppInCoeff = pInCoeff * 0.5f; // 0 ... 1
pOutCoeff = (-2.0f * cosTwoPiFreqDivSR) * coeffScalar; // -2 ... 2
ppOutCoeff = (1.0f - slopeFactor) * coeffScalar; // 1 ... 0 ... 1
}
//------------------------------------------------------------------------
void IIRfilter::calculateHighpassCoefficients(float cutoff, float samplerate)
{
float twoPiFreqDivSR, cosTwoPiFreqDivSR, Q, slopeFactor, coeffScalar;
Q = 0.5f;
twoPiFreqDivSR = 2.0f * PI * cutoff / samplerate; // ¹ ... 0
cosTwoPiFreqDivSR = cosf(twoPiFreqDivSR); // 1 ... -1
slopeFactor = sinf(twoPiFreqDivSR) / (Q * 2.0f); // 0 ... 1 ... 0
coeffScalar = 1.0f / (1.0f + slopeFactor); // 1 ... 0.5 ... 1
// calculate filter coefficients
pInCoeff = (-1.0f - cosTwoPiFreqDivSR) * coeffScalar; // 2 ... 0
inCoeff = ppInCoeff = pInCoeff * (-0.5f); // -1 ... 0
pOutCoeff = (-2.0f * cosTwoPiFreqDivSR) * coeffScalar; // -2 ... 2
ppOutCoeff = (1.0f - slopeFactor) * coeffScalar; // 1 ... 0 ... 1
}
//------------------------------------------------------------------------
void IIRfilter::copyCoefficients(IIRfilter *source)
{
pOutCoeff = source->pOutCoeff;
ppOutCoeff = source->ppOutCoeff;
pInCoeff = source->pInCoeff;
ppInCoeff = source->ppInCoeff;
inCoeff = source->inCoeff;
}
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