1 files changed, 38 insertions, 0 deletions
diff --git a/intern/audaspace/FX/AUD_ButterworthCalculator.cpp b/intern/audaspace/FX/AUD_ButterworthCalculator.cpp
new file mode 100644
index 00000000000..7a3c6f71e15
--- /dev/null
+++ b/intern/audaspace/FX/AUD_ButterworthCalculator.cpp
@@ -0,0 +1,38 @@
+#include "AUD_ButterworthCalculator.h"
+
+#include <cmath>
+
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
+#define BWPB41 0.76536686473
+#define BWPB42 1.84775906502
+
+AUD_ButterworthCalculator::AUD_ButterworthCalculator(float frequency) :
+	m_frequency(frequency)
+{
+}
+
+void AUD_ButterworthCalculator::recalculateCoefficients(AUD_SampleRate rate, std::vector<float> &b, std::vector<float> &a)
+{
+	float omega = 2 * tan(m_frequency * M_PI / rate);
+	float o2 = omega * omega;
+	float o4 = o2 * o2;
+	float x1 = o2 + 2.0f * (float)BWPB41 * omega + 4.0f;
+	float x2 = o2 + 2.0f * (float)BWPB42 * omega + 4.0f;
+	float y1 = o2 - 2.0f * (float)BWPB41 * omega + 4.0f;
+	float y2 = o2 - 2.0f * (float)BWPB42 * omega + 4.0f;
+	float o228 = 2.0f * o2 - 8.0f;
+	float norm = x1 * x2;
+	a.push_back(1);
+	a.push_back((x1 + x2) * o228 / norm);
+	a.push_back((x1 * y2 + x2 * y1 + o228 * o228) / norm);
+	a.push_back((y1 + y2) * o228 / norm);
+	a.push_back(y1 * y2 / norm);
+	b.push_back(o4 / norm);
+	b.push_back(4 * o4 / norm);
+	b.push_back(6 * o4 / norm);
+	b.push_back(b[1]);
+	b.push_back(b[0]);
+}