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sdrangel/sdrbase/dsp/interpolator.cpp
2018-12-09 22:11:39 +01:00

176 lines
3.6 KiB
C++

#define _USE_MATH_DEFINES
#include <math.h>
#include <vector>
#include "dsp/interpolator.h"
void Interpolator::createPolyphaseLowPass(
std::vector<Real>& taps,
int phaseSteps,
double gain,
double sampleRateHz,
double cutoffFreqHz,
double transitionWidthHz,
double oobAttenuationdB)
{
double nbTapsPerPhase = (oobAttenuationdB * sampleRateHz) / (22.0 * transitionWidthHz * phaseSteps);
return createPolyphaseLowPass(taps, phaseSteps, gain, sampleRateHz, cutoffFreqHz, nbTapsPerPhase);
}
void Interpolator::createPolyphaseLowPass(
std::vector<Real>& taps,
int phaseSteps,
double gain,
double sampleRateHz,
double cutoffFreqHz,
double nbTapsPerPhase)
{
int ntaps = (int)(nbTapsPerPhase * phaseSteps);
qDebug("Interpolator::createPolyphaseLowPass: ntaps: %d", ntaps);
if ((ntaps % 2) != 0) {
ntaps++;
}
ntaps *= phaseSteps;
taps.resize(ntaps);
std::vector<float> window(ntaps);
for (int n = 0; n < ntaps; n++) {
window[n] = 0.54 - 0.46 * cos ((2 * M_PI * n) / (ntaps - 1));
}
int M = (ntaps - 1) / 2;
double fwT0 = 2 * M_PI * cutoffFreqHz / sampleRateHz;
for (int n = -M; n <= M; n++)
{
if (n == 0) {
taps[n + M] = fwT0 / M_PI * window[n + M];
} else {
taps[n + M] = sin (n * fwT0) / (n * M_PI) * window[n + M];
}
}
double max = taps[0 + M];
for (int n = 1; n <= M; n++) {
max += 2.0 * taps[n + M];
}
gain /= max;
for (int i = 0; i < ntaps; i++) {
taps[i] *= gain;
}
}
Interpolator::Interpolator() :
m_taps(0),
m_alignedTaps(0),
m_taps2(0),
m_alignedTaps2(0),
m_ptr(0),
m_phaseSteps(1),
m_nTaps(1)
{
}
Interpolator::~Interpolator()
{
free();
}
void Interpolator::create(int phaseSteps, double sampleRate, double cutoff, double nbTapsPerPhase)
{
free();
std::vector<Real> taps;
createPolyphaseLowPass(
taps,
phaseSteps, // number of polyphases
1.0, // gain
phaseSteps * sampleRate, // sampling frequency
cutoff, // hz beginning of transition band
nbTapsPerPhase);
// init state
m_ptr = 0;
m_nTaps = taps.size() / phaseSteps;
m_phaseSteps = phaseSteps;
m_samples.resize(m_nTaps + 2);
for (int i = 0; i < m_nTaps + 2; i++) {
m_samples[i] = 0;
}
// reorder into polyphase
std::vector<Real> polyphase(taps.size());
for (int phase = 0; phase < phaseSteps; phase++)
{
for (int i = 0; i < m_nTaps; i++) {
polyphase[phase * m_nTaps + i] = taps[i * phaseSteps + phase];
}
}
// normalize phase filters
for (int phase = 0; phase < phaseSteps; phase++)
{
Real sum = 0;
for (int i = phase * m_nTaps; i < phase * m_nTaps + m_nTaps; i++) {
sum += polyphase[i];
}
for (int i = phase * m_nTaps; i < phase * m_nTaps + m_nTaps; i++) {
polyphase[i] /= sum;
}
}
// move taps around to match sse storage requirements
m_taps = new float[2 * taps.size() + 8];
for (uint i = 0; i < 2 * taps.size() + 8; ++i) {
m_taps[i] = 0;
}
m_alignedTaps = (float*)((((quint64)m_taps) + 15) & ~15);
for (uint i = 0; i < taps.size(); ++i)
{
m_alignedTaps[2 * i + 0] = polyphase[i];
m_alignedTaps[2 * i + 1] = polyphase[i];
}
m_taps2 = new float[2 * taps.size() + 8];
for (uint i = 0; i < 2 * taps.size() + 8; ++i) {
m_taps2[i] = 0;
}
m_alignedTaps2 = (float*)((((quint64)m_taps2) + 15) & ~15);
for (uint i = 1; i < taps.size(); ++i)
{
m_alignedTaps2[2 * (i - 1) + 0] = polyphase[i];
m_alignedTaps2[2 * (i - 1) + 1] = polyphase[i];
}
}
void Interpolator::free()
{
if (m_taps != NULL)
{
delete[] m_taps;
m_taps = NULL;
m_alignedTaps = NULL;
delete[] m_taps2;
m_taps2 = NULL;
m_alignedTaps2 = NULL;
}
}