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/* FM modulation processing
*
* (C) 2017 by Andreas Eversberg <jolly@eversberg.eu>
* All Rights Reserved
*
* This program 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.
*
* This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#include "sample.h"
#include "iir_filter.h"
#include "fm_modulation.h"
//#define FAST_SINE
/* init FM modulator */
void fm_mod_init(fm_mod_t *mod, double samplerate, double offset, double amplitude)
{
memset(mod, 0, sizeof(*mod));
mod->samplerate = samplerate;
mod->offset = offset;
mod->amplitude = amplitude;
#ifdef FAST_SINE
int i;
mod->sin_tab = calloc(65536+16384, sizeof(*mod->sin_tab));
if (!mod->sin_tab) {
fprintf(stderr, "No mem!\n");
abort();
}
/* generate sine and cosine */
for (i = 0; i < 65536+16384; i++)
mod->sin_tab[i] = sin(2.0 * M_PI * (double)i / 65536.0) * amplitude;
#endif
}
/* do frequency modulation of samples and add them to existing buff */
void fm_modulate(fm_mod_t *mod, sample_t *samples, int num, float *buff)
{
double dev, rate, phase, offset;
int s, ss;
#ifdef FAST_SINE
double *sin_tab, *cos_tab;
#else
double amplitude;
#endif
rate = mod->samplerate;
phase = mod->phase;
offset = mod->offset;
#ifdef FAST_SINE
sin_tab = mod->sin_tab;
cos_tab = mod->sin_tab + 16384;
#else
amplitude = mod->amplitude;
#endif
/* modulate */
for (s = 0, ss = 0; s < num; s++) {
/* deviation is defined by the sample value and the offset */
dev = offset + samples[s];
#ifdef FAST_SINE
phase += 65536.0 * dev / rate;
if (phase < 0.0)
phase += 65536.0;
else if (phase >= 65536.0)
phase -= 65536.0;
buff[ss++] += cos_tab[(uint16_t)phase];
buff[ss++] += sin_tab[(uint16_t)phase];
#else
phase += 2.0 * M_PI * dev / rate;
if (phase < 0.0)
phase += 2.0 * M_PI;
else if (phase >= 2.0 * M_PI)
phase -= 2.0 * M_PI;
buff[ss++] += cos(phase) * amplitude;
buff[ss++] += sin(phase) * amplitude;
#endif
}
mod->phase = phase;
}
/* init FM demodulator */
void fm_demod_init(fm_demod_t *demod, double samplerate, double offset, double bandwidth)
{
memset(demod, 0, sizeof(*demod));
demod->samplerate = samplerate;
#ifdef FAST_SINE
demod->rot = 65536.0 * -offset / samplerate;
#else
demod->rot = 2 * M_PI * -offset / samplerate;
#endif
/* use fourth order (2 iter) filter, since it is as fast as second order (1 iter) filter */
iir_lowpass_init(&demod->lp[0], bandwidth / 2.0, samplerate, 2);
iir_lowpass_init(&demod->lp[1], bandwidth / 2.0, samplerate, 2);
#ifdef FAST_SINE
int i;
demod->sin_tab = calloc(65536+16384, sizeof(*demod->sin_tab));
if (!demod->sin_tab) {
fprintf(stderr, "No mem!\n");
abort();
}
/* generate sine and cosine */
for (i = 0; i < 65536+16384; i++)
demod->sin_tab[i] = sin(2.0 * M_PI * (double)i / 65536.0);
#endif
}
/* do frequency demodulation of buff and write them to samples */
void fm_demodulate(fm_demod_t *demod, sample_t *samples, int num, float *buff)
{
double phase, rot, last_phase, dev, rate;
double _sin, _cos;
sample_t I[num], Q[num], i, q;
int s, ss;
#ifdef FAST_SINE
double *sin_tab, *cos_tab;
#endif
rate = demod->samplerate;
phase = demod->phase;
rot = demod->rot;
#ifdef FAST_SINE
sin_tab = demod->sin_tab;
cos_tab = demod->sin_tab + 16384;
#endif
for (s = 0, ss = 0; s < num; s++) {
phase += rot;
i = buff[ss++];
q = buff[ss++];
#ifdef FAST_SINE
if (phase < 0.0)
phase += 65536.0;
else if (phase >= 65536.0)
phase -= 65536.0;
_sin = sin_tab[(uint16_t)phase];
_cos = cos_tab[(uint16_t)phase];
#else
if (phase < 0.0)
phase += 2.0 * M_PI;
else if (phase >= 2.0 * M_PI)
phase -= 2.0 * M_PI;
_sin = sin(phase);
_cos = cos(phase);
#endif
I[s] = i * _cos - q * _sin;
Q[s] = i * _sin + q * _cos;
}
demod->phase = phase;
iir_process(&demod->lp[0], I, num);
iir_process(&demod->lp[1], Q, num);
last_phase = demod->last_phase;
for (s = 0; s < num; s++) {
phase = atan2(Q[s], I[s]);
dev = (phase - last_phase) / 2 / M_PI;
last_phase = phase;
if (dev < -0.49)
dev += 1.0;
else if (dev > 0.49)
dev -= 1.0;
dev *= rate;
samples[s] = dev;
}
demod->last_phase = last_phase;
}
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