206214ce2b
Improves sound - blip_buf was altering the audio output quite a bit compared to the DSP's raw output
76 lines
2.2 KiB
C++
76 lines
2.2 KiB
C++
#include "stdafx.h"
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#include "HermiteResampler.h"
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//Adapted from http://paulbourke.net/miscellaneous/interpolation/
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//Original author: Paul Bourke ("Any source code found here may be freely used provided credits are given to the author.")
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int16_t HermiteResampler::HermiteInterpolate(double values[4], double mu)
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{
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constexpr double tension = 0; //Tension: 1 is high, 0 normal, -1 is low
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constexpr double bias = 0; //Bias: 0 is even, positive is towards first segment, negative towards the other
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double m0, m1, mu2, mu3;
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double a0, a1, a2, a3;
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mu2 = mu * mu;
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mu3 = mu2 * mu;
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m0 = (values[1] - values[0]) * (1 + bias) * (1 - tension) / 2;
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m0 += (values[2] - values[1]) * (1 - bias) * (1 - tension) / 2;
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m1 = (values[2] - values[1]) * (1 + bias) * (1 - tension) / 2;
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m1 += (values[3] - values[2]) * (1 - bias) * (1 - tension) / 2;
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a0 = 2 * mu3 - 3 * mu2 + 1;
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a1 = mu3 - 2 * mu2 + mu;
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a2 = mu3 - mu2;
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a3 = -2 * mu3 + 3 * mu2;
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double output = a0 * values[1] + a1 * m0 + a2 * m1 + a3 * values[2];
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return (int16_t)std::max(std::min(output, 32767.0), -32768.0);
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}
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void HermiteResampler::PushSample(double prevValues[4], int16_t sample)
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{
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prevValues[0] = prevValues[1];
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prevValues[1] = prevValues[2];
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prevValues[2] = prevValues[3];
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prevValues[3] = (double)sample;
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}
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void HermiteResampler::Reset()
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{
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for(int i = 0; i < 4; i++) {
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_prevLeft[i] = 0.0;
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_prevRight[i] = 0.0;
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}
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_fraction = 0.0;
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}
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void HermiteResampler::SetSampleRates(double srcRate, double dstRate)
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{
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_rateRatio = srcRate / dstRate;
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}
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uint32_t HermiteResampler::Resample(int16_t* in, uint32_t inSampleCount, int16_t* out)
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{
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if(_rateRatio == 1.0) {
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memcpy(out, in, inSampleCount * 2 * sizeof(int16_t));
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return inSampleCount;
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}
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uint32_t outPos = 0;
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for(uint32_t i = 0; i < inSampleCount * 2; i += 2) {
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while(_fraction <= 1.0) {
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//Generate interpolated samples until we have enough samples for the current source sample
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out[outPos] = HermiteInterpolate(_prevLeft, _fraction);
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out[outPos + 1] = HermiteInterpolate(_prevRight, _fraction);
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outPos += 2;
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_fraction += _rateRatio;
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}
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//Move to the next source sample
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PushSample(_prevLeft, in[i]);
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PushSample(_prevRight, in[i + 1]);
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_fraction -= 1.0;
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}
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return outPos / 2;
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}
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