LowpassFilter.cpp

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//=====================================================================================
//=====================================================================================
 
#include "LowpassFilter.h"
 
//=====================================================================================
krotos::LowpassFilter::LowpassFilter() : x_1(0), x_2(0), y_1(0), y_2(0) { configure(0.3f); }
 
//=====================================================================================
void krotos::LowpassFilter::configure(float normalisedCutoff)
{
    assert(normalisedCutoff <= 0.5);
    assert(normalisedCutoff >= 0.0);
 
    float K = static_cast<float>(tan(M_PI * normalisedCutoff));
 
    float denominator = 1.f + sqrtf(2.f) * K + (K * K);
 
    b0 = (K * K) / denominator;
    b1 = (2.f * K * K) / denominator;
    b2 = b0;
    a1 = (2.f * (K * K - 1.f)) / denominator;
    a2 = (1.f - sqrtf(2.f) * K + (K * K)) / denominator;
}
 
//=====================================================================================
float krotos::LowpassFilter::processSample(float x)
{
    float y = b0 * x + b1 * x_1 + b2 * x_2 - a1 * y_1 - a2 * y_2;
 
    x_2 = x_1;
    x_1 = x;
    y_2 = y_1;
    y_1 = y;
 
    return y;
}