forked from bartvdbraak/blender
39 lines
1.1 KiB
C++
39 lines
1.1 KiB
C++
#include "AUD_ButterworthCalculator.h"
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#include <cmath>
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#ifndef M_PI
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#define M_PI 3.14159265358979323846
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#endif
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#define BWPB41 0.76536686473
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#define BWPB42 1.84775906502
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AUD_ButterworthCalculator::AUD_ButterworthCalculator(float frequency) :
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m_frequency(frequency)
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{
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}
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void AUD_ButterworthCalculator::recalculateCoefficients(AUD_SampleRate rate, std::vector<float> &b, std::vector<float> &a)
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{
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float omega = 2 * tan(m_frequency * M_PI / rate);
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float o2 = omega * omega;
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float o4 = o2 * o2;
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float x1 = o2 + 2.0f * (float)BWPB41 * omega + 4.0f;
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float x2 = o2 + 2.0f * (float)BWPB42 * omega + 4.0f;
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float y1 = o2 - 2.0f * (float)BWPB41 * omega + 4.0f;
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float y2 = o2 - 2.0f * (float)BWPB42 * omega + 4.0f;
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float o228 = 2.0f * o2 - 8.0f;
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float norm = x1 * x2;
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a.push_back(1);
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a.push_back((x1 + x2) * o228 / norm);
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a.push_back((x1 * y2 + x2 * y1 + o228 * o228) / norm);
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a.push_back((y1 + y2) * o228 / norm);
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a.push_back(y1 * y2 / norm);
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b.push_back(o4 / norm);
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b.push_back(4 * o4 / norm);
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b.push_back(6 * o4 / norm);
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b.push_back(b[1]);
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b.push_back(b[0]);
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}
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