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SourMesen
3b76e5df9b
The hermite resampler used did not apply a lowpass filter when downsampling, which caused aliasing. This was easier to notice when setting the output sample rate to 11kHz in the settings since this increases the gap between the core's sample rate & the output rate.
56 lines
1.1 KiB
C++
56 lines
1.1 KiB
C++
#include "pch.h"
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#include "BiquadFilter.h"
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#include <cmath>
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void BiquadFilter::Init(double srcRate, double dstRate, double q)
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{
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if(dstRate >= srcRate) {
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//Disable filter when no downsampling is done
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_b0 = 1;
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_b1 = 0;
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_b2 = 0;
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_a1 = 0;
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_a2 = 0;
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return;
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}
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constexpr double PI = 3.14159265358979323846;
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double cutoffFreq = dstRate / 2.0;
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double w = 2.0 * PI * cutoffFreq / srcRate;
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double s = std::sin(w);
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double c = std::cos(w);
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double alpha = s / (2.0 * q);
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double a0 = 1.0 + alpha;
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_b0 = ((1.0 - c) / 2.0) / a0;
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_b1 = (1.0 - c) / a0;
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_b2 = ((1.0 - c) / 2.0) / a0;
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_a1 = (-2.0 * c) / a0;
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_a2 = (1.0 - alpha) / a0;
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}
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double BiquadFilter::ProcessLeft(double in)
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{
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double out = (in * _b0) + _d0Left;
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_d0Left = (in * _b1) - (out * _a1) + _d1Left;
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_d1Left = (in * _b2) - (out * _a2);
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return out;
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}
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double BiquadFilter::ProcessRight(double in)
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{
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double out = (in * _b0) + _d0Right;
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_d0Right = (in * _b1) - (out * _a1) + _d1Right;
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_d1Right = (in * _b2) - (out * _a2);
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return out;
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}
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void BiquadFilter::Reset()
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{
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_d0Left = 0;
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_d1Left = 0;
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_d0Right = 0;
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_d1Right = 0;
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}
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