mirror of https://github.com/bsnes-emu/bsnes.git
45 lines
1.0 KiB
C++
45 lines
1.0 KiB
C++
#pragma once
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//one-pole first-order IIR filter
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namespace nall { namespace DSP { namespace IIR {
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struct OnePole {
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enum class Type : uint {
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LowPass,
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HighPass,
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};
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inline auto reset(Type type, double cutoffFrequency, double samplingFrequency) -> void;
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inline auto process(double in) -> double; //normalized sample (-1.0 to +1.0)
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private:
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Type type;
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double cutoffFrequency;
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double samplingFrequency;
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double a0, b1; //coefficients
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double z1; //first-order IIR
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};
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auto OnePole::reset(Type type, double cutoffFrequency, double samplingFrequency) -> void {
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this->type = type;
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this->cutoffFrequency = cutoffFrequency;
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this->samplingFrequency = samplingFrequency;
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z1 = 0.0;
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double x = cos(2.0 * Math::Pi * cutoffFrequency / samplingFrequency);
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if(type == Type::LowPass) {
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b1 = +2.0 - x - sqrt((+2.0 - x) * (+2.0 - x) - 1);
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a0 = 1.0 - b1;
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} else {
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b1 = -2.0 - x + sqrt((-2.0 - x) * (-2.0 - x) - 1);
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a0 = 1.0 + b1;
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}
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}
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auto OnePole::process(double in) -> double {
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return z1 = in * a0 + z1 * b1;
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}
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}}}
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