mirror of
https://github.com/f4exb/sdrangel.git
synced 2024-08-29 17:26:33 -04:00
322 lines
7.4 KiB
C++
322 lines
7.4 KiB
C++
// ----------------------------------------------------------------------------
|
|
// fftfilt.cxx -- Fast convolution Overlap-Add filter
|
|
//
|
|
// Filter implemented using overlap-add FFT convolution method
|
|
// h(t) characterized by Windowed-Sinc impulse response
|
|
//
|
|
// Reference:
|
|
// "The Scientist and Engineer's Guide to Digital Signal Processing"
|
|
// by Dr. Steven W. Smith, http://www.dspguide.com
|
|
// Chapters 16, 18 and 21
|
|
//
|
|
// Copyright (C) 2006-2008 Dave Freese, W1HKJ
|
|
//
|
|
// This file is part of fldigi.
|
|
//
|
|
// Fldigi is free software: you can redistribute it and/or modify
|
|
// it under the terms of the GNU General Public License as published by
|
|
// the Free Software Foundation, either version 3 of the License, or
|
|
// (at your option) any later version.
|
|
//
|
|
// Fldigi is distributed in the hope that it will be useful,
|
|
// but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
// GNU General Public License for more details.
|
|
//
|
|
// You should have received a copy of the GNU General Public License
|
|
// along with fldigi. If not, see <http://www.gnu.org/licenses/>.
|
|
// ----------------------------------------------------------------------------
|
|
|
|
#include <memory.h>
|
|
#include <iostream>
|
|
#include <fstream>
|
|
#include <cstdlib>
|
|
#include <cmath>
|
|
#include <typeinfo>
|
|
|
|
#include <stdio.h>
|
|
#include <sys/types.h>
|
|
#include <unistd.h>
|
|
#include <memory.h>
|
|
|
|
#include <dsp/misc.h>
|
|
#include <dsp/fftfilt.h>
|
|
|
|
//------------------------------------------------------------------------------
|
|
// initialize the filter
|
|
// create forward and reverse FFTs
|
|
//------------------------------------------------------------------------------
|
|
|
|
// Only need a single instance of g_fft, used for both forward and reverse
|
|
void fftfilt::init_filter()
|
|
{
|
|
flen2 = flen >> 1;
|
|
fft = new g_fft<float>(flen);
|
|
|
|
filter = new cmplx[flen];
|
|
data = new cmplx[flen];
|
|
output = new cmplx[flen2];
|
|
ovlbuf = new cmplx[flen2];
|
|
|
|
memset(filter, 0, flen * sizeof(cmplx));
|
|
memset(data, 0, flen * sizeof(cmplx));
|
|
memset(output, 0, flen2 * sizeof(cmplx));
|
|
memset(ovlbuf, 0, flen2 * sizeof(cmplx));
|
|
|
|
inptr = 0;
|
|
}
|
|
|
|
//------------------------------------------------------------------------------
|
|
// fft filter
|
|
// f1 < f2 ==> band pass filter
|
|
// f1 > f2 ==> band reject filter
|
|
// f1 == 0 ==> low pass filter
|
|
// f2 == 0 ==> high pass filter
|
|
//------------------------------------------------------------------------------
|
|
fftfilt::fftfilt(float f1, float f2, int len)
|
|
{
|
|
flen = len;
|
|
init_filter();
|
|
create_filter(f1, f2);
|
|
}
|
|
|
|
fftfilt::fftfilt(float f2, int len)
|
|
{
|
|
flen = len;
|
|
init_filter();
|
|
create_dsb_filter(f2);
|
|
}
|
|
|
|
fftfilt::~fftfilt()
|
|
{
|
|
if (fft) delete fft;
|
|
|
|
if (filter) delete [] filter;
|
|
if (data) delete [] data;
|
|
if (output) delete [] output;
|
|
if (ovlbuf) delete [] ovlbuf;
|
|
}
|
|
|
|
void fftfilt::create_filter(float f1, float f2)
|
|
{
|
|
// initialize the filter to zero
|
|
memset(filter, 0, flen * sizeof(cmplx));
|
|
|
|
// create the filter shape coefficients by fft
|
|
bool b_lowpass, b_highpass;
|
|
b_lowpass = (f2 != 0);
|
|
b_highpass = (f1 != 0);
|
|
|
|
for (int i = 0; i < flen2; i++) {
|
|
filter[i] = 0;
|
|
// lowpass @ f2
|
|
if (b_lowpass)
|
|
filter[i] += fsinc(f2, i, flen2);
|
|
// highighpass @ f1
|
|
if (b_highpass)
|
|
filter[i] -= fsinc(f1, i, flen2);
|
|
}
|
|
// highpass is delta[flen2/2] - h(t)
|
|
if (b_highpass && f2 < f1)
|
|
filter[flen2 / 2] += 1;
|
|
|
|
for (int i = 0; i < flen2; i++)
|
|
filter[i] *= _blackman(i, flen2);
|
|
|
|
fft->ComplexFFT(filter);
|
|
|
|
// normalize the output filter for unity gain
|
|
float scale = 0, mag;
|
|
for (int i = 0; i < flen2; i++) {
|
|
mag = abs(filter[i]);
|
|
if (mag > scale) scale = mag;
|
|
}
|
|
if (scale != 0) {
|
|
for (int i = 0; i < flen; i++)
|
|
filter[i] /= scale;
|
|
}
|
|
}
|
|
|
|
// Double the size of FFT used for equivalent SSB filter or assume FFT is half the size of the one used for SSB
|
|
void fftfilt::create_dsb_filter(float f2)
|
|
{
|
|
// initialize the filter to zero
|
|
memset(filter, 0, flen * sizeof(cmplx));
|
|
|
|
for (int i = 0; i < flen2; i++) {
|
|
filter[i] = fsinc(f2, i, flen2);
|
|
filter[i] *= _blackman(i, flen2);
|
|
}
|
|
|
|
fft->ComplexFFT(filter);
|
|
|
|
// normalize the output filter for unity gain
|
|
float scale = 0, mag;
|
|
for (int i = 0; i < flen2; i++) {
|
|
mag = abs(filter[i]);
|
|
if (mag > scale) scale = mag;
|
|
}
|
|
if (scale != 0) {
|
|
for (int i = 0; i < flen; i++)
|
|
filter[i] /= scale;
|
|
}
|
|
}
|
|
|
|
// test bypass
|
|
int fftfilt::noFilt(const cmplx & in, cmplx **out)
|
|
{
|
|
data[inptr++] = in;
|
|
if (inptr < flen2)
|
|
return 0;
|
|
inptr = 0;
|
|
|
|
*out = data;
|
|
return flen2;
|
|
}
|
|
|
|
// Filter with fast convolution (overlap-add algorithm).
|
|
int fftfilt::runFilt(const cmplx & in, cmplx **out)
|
|
{
|
|
data[inptr++] = in;
|
|
if (inptr < flen2)
|
|
return 0;
|
|
inptr = 0;
|
|
|
|
fft->ComplexFFT(data);
|
|
for (int i = 0; i < flen; i++)
|
|
data[i] *= filter[i];
|
|
|
|
fft->InverseComplexFFT(data);
|
|
|
|
for (int i = 0; i < flen2; i++) {
|
|
output[i] = ovlbuf[i] + data[i];
|
|
ovlbuf[i] = data[flen2 + i];
|
|
}
|
|
memset (data, 0, flen * sizeof(cmplx));
|
|
|
|
*out = output;
|
|
return flen2;
|
|
}
|
|
|
|
// Second version for single sideband
|
|
int fftfilt::runSSB(const cmplx & in, cmplx **out, bool usb)
|
|
{
|
|
data[inptr++] = in;
|
|
if (inptr < flen2)
|
|
return 0;
|
|
inptr = 0;
|
|
|
|
fft->ComplexFFT(data);
|
|
|
|
// Discard frequencies for ssb
|
|
if ( usb )
|
|
for (int i = 0; i < flen2; i++) {
|
|
data[i] *= filter[i];
|
|
data[flen2 + i] = 0;
|
|
}
|
|
else
|
|
for (int i = 0; i < flen2; i++) {
|
|
data[i] = 0;
|
|
data[flen2 + i] *= filter[flen2 + i];
|
|
}
|
|
|
|
// in-place FFT: freqdata overwritten with filtered timedata
|
|
fft->InverseComplexFFT(data);
|
|
|
|
// overlap and add
|
|
for (int i = 0; i < flen2; i++) {
|
|
output[i] = ovlbuf[i] + data[i];
|
|
ovlbuf[i] = data[i+flen2];
|
|
}
|
|
memset (data, 0, flen * sizeof(cmplx));
|
|
|
|
*out = output;
|
|
return flen2;
|
|
}
|
|
|
|
// Version for double sideband. You have to double the FFT size used for SSB.
|
|
int fftfilt::runDSB(const cmplx & in, cmplx **out)
|
|
{
|
|
data[inptr++] = in;
|
|
if (inptr < flen2)
|
|
return 0;
|
|
inptr = 0;
|
|
|
|
fft->ComplexFFT(data);
|
|
|
|
for (int i = 0; i < flen2; i++) {
|
|
data[i] *= filter[i];
|
|
data[flen2 + i] *= filter[flen2 + i];
|
|
}
|
|
|
|
// in-place FFT: freqdata overwritten with filtered timedata
|
|
fft->InverseComplexFFT(data);
|
|
|
|
// overlap and add
|
|
for (int i = 0; i < flen2; i++) {
|
|
output[i] = ovlbuf[i] + data[i];
|
|
ovlbuf[i] = data[i+flen2];
|
|
}
|
|
|
|
memset (data, 0, flen * sizeof(cmplx));
|
|
|
|
*out = output;
|
|
return flen2;
|
|
}
|
|
|
|
/* Sliding FFT from Fldigi */
|
|
|
|
struct sfft::vrot_bins_pair {
|
|
cmplx vrot;
|
|
cmplx bins;
|
|
} ;
|
|
|
|
sfft::sfft(int len)
|
|
{
|
|
vrot_bins = new vrot_bins_pair[len];
|
|
delay = new cmplx[len];
|
|
fftlen = len;
|
|
first = 0;
|
|
last = len - 1;
|
|
ptr = 0;
|
|
double phi = 0.0, tau = 2.0 * M_PI/ len;
|
|
k2 = 1.0;
|
|
for (int i = 0; i < len; i++) {
|
|
vrot_bins[i].vrot = cmplx( K1 * cos (phi), K1 * sin (phi) );
|
|
phi += tau;
|
|
delay[i] = vrot_bins[i].bins = 0.0;
|
|
k2 *= K1;
|
|
}
|
|
}
|
|
|
|
sfft::~sfft()
|
|
{
|
|
delete [] vrot_bins;
|
|
delete [] delay;
|
|
}
|
|
|
|
// Sliding FFT, cmplx input, cmplx output
|
|
// FFT is computed for each value from first to last
|
|
// Values are not stable until more than "len" samples have been processed.
|
|
void sfft::run(const cmplx& input)
|
|
{
|
|
cmplx & de = delay[ptr];
|
|
const cmplx z( input.real() - k2 * de.real(), input.imag() - k2 * de.imag());
|
|
de = input;
|
|
|
|
if (++ptr >= fftlen)
|
|
ptr = 0;
|
|
|
|
for (vrot_bins_pair *itr = vrot_bins + first, *end = vrot_bins + last; itr != end ; ++itr)
|
|
itr->bins = (itr->bins + z) * itr->vrot;
|
|
}
|
|
|
|
// Copies the frequencies to a pointer.
|
|
void sfft::fetch(float *result)
|
|
{
|
|
for (vrot_bins_pair *itr = vrot_bins, *end = vrot_bins + last; itr != end; ++itr, ++result)
|
|
*result = itr->bins.real() * itr->bins.real()
|
|
+ itr->bins.imag() * itr->bins.imag();
|
|
}
|
|
|