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#include "AUD_LowpassCalculator.h"
#include <cmath>
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
AUD_LowpassCalculator::AUD_LowpassCalculator(float frequency, float Q) :
m_frequency(frequency),
m_Q(Q)
{
}
void AUD_LowpassCalculator::recalculateCoefficients(AUD_SampleRate rate, std::vector<float> &b, std::vector<float> &a)
{
float w0 = 2 * M_PI * m_frequency / rate;
float alpha = sin(w0) / (2 * m_Q);
float norm = 1 + alpha;
float c = cos(w0);
a.push_back(1);
a.push_back(-2 * c / norm);
a.push_back((1 - alpha) / norm);
b.push_back((1 - c) / (2 * norm));
b.push_back((1 - c) / norm);
b.push_back(b[0]);
}
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