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sdrangel/sdrbase/dsp/bandpass.h

131 lines
2.6 KiB
C++

#ifndef INCLUDE_BANDPASS_H
#define INCLUDE_BANDPASS_H
#define _USE_MATH_DEFINES
#include <math.h>
#include "dsp/dsptypes.h"
#undef M_PI
#define M_PI 3.14159265358979323846
template <class Type> class Bandpass {
public:
Bandpass() : m_ptr(0) { }
void create(int nTaps, double sampleRate, double lowCutoff, double highCutoff)
{
std::vector<Real> taps_lp;
std::vector<Real> taps_hp;
double wcl = 2.0 * M_PI * lowCutoff;
double Wcl = wcl / sampleRate;
double wch = 2.0 * M_PI * highCutoff;
double Wch = wch / sampleRate;
int i;
// check constraints
if(!(nTaps & 1)) {
qDebug("Bandpass filter has to have an odd number of taps");
nTaps++;
}
// make room
m_samples.resize(nTaps);
for(int i = 0; i < nTaps; i++)
m_samples[i] = 0;
m_ptr = 0;
m_taps.resize(nTaps / 2 + 1);
taps_lp.resize(nTaps / 2 + 1);
taps_hp.resize(nTaps / 2 + 1);
// generate Sinc filter core
for(i = 0; i < nTaps / 2 + 1; i++) {
if(i == (nTaps - 1) / 2) {
taps_lp[i] = Wch / M_PI;
taps_hp[i] = -(Wcl / M_PI);
}
else {
taps_lp[i] = sin(((double)i - ((double)nTaps - 1.0) / 2.0) * Wch) / (((double)i - ((double)nTaps - 1.0) / 2.0) * M_PI);
taps_hp[i] = -sin(((double)i - ((double)nTaps - 1.0) / 2.0) * Wcl) / (((double)i - ((double)nTaps - 1.0) / 2.0) * M_PI);
}
}
taps_hp[(nTaps - 1) / 2] += 1;
// apply Hamming window and combine lowpass and highpass
for(i = 0; i < nTaps / 2 + 1; i++) {
taps_lp[i] *= 0.54 + 0.46 * cos((2.0 * M_PI * ((double)i - ((double)nTaps - 1.0) / 2.0)) / (double)nTaps);
taps_hp[i] *= 0.54 + 0.46 * cos((2.0 * M_PI * ((double)i - ((double)nTaps - 1.0) / 2.0)) / (double)nTaps);
m_taps[i] = -(taps_lp[i]+taps_hp[i]);
}
m_taps[(nTaps - 1) / 2] += 1;
// normalize
Real sum = 0;
for(i = 0; i < (int)m_taps.size() - 1; i++) {
sum += m_taps[i] * 2;
}
sum += m_taps[i];
for(i = 0; i < (int)m_taps.size(); i++) {
m_taps[i] /= sum;
}
}
Type filter(Type sample)
{
Type acc = 0;
int a = m_ptr;
int b = a - 1;
int i, n_taps, size;
m_samples[m_ptr] = sample;
size = m_samples.size(); // Valgrind optim (2)
while(b < 0)
{
b += size;
}
n_taps = m_taps.size() - 1; // Valgrind optim
for(i = 0; i < n_taps; i++)
{
acc += (m_samples[a] + m_samples[b]) * m_taps[i];
a++;
while (a >= size)
{
a -= size;
}
b--;
while(b < 0)
{
b += size;
}
}
acc += m_samples[a] * m_taps[i];
m_ptr++;
while (m_ptr >= size)
{
m_ptr -= size;
}
return acc;
}
private:
std::vector<Real> m_taps;
std::vector<Type> m_samples;
int m_ptr;
};
#endif // INCLUDE_BANDPASS_H