1 files changed, 61 insertions, 0 deletions

diff --git a/dfx-library/IIRfilter.cpp b/dfx-library/IIRfilter.cpp
new file mode 100755
index 0000000..d78bf2f
--- /dev/null
+++ b/dfx-library/IIRfilter.cpp
@@ -0,0 +1,61 @@
+#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;
+}