39 lines
1.1 KiB
C++
39 lines
1.1 KiB
C++
#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]);
|
|
}
|