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Better Stereo FM implementation using liquid-dsp tools

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This commit is contained in:
Charles J. Cliffe 2014-12-27 12:23:09 -05:00
parent 06103a2d1b
commit 376ddfad98
1 changed files with 25 additions and 11 deletions
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36
src/demod/DemodulatorThread.cpp
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@ -34,6 +34,16 @@ void DemodulatorThread::threadMain() {
msresamp_rrrf stereo_resampler = NULL; msresamp_rrrf stereo_resampler = NULL;
msresamp_crcf resampler = NULL; msresamp_crcf resampler = NULL;
unsigned int m=5; // filter semi-length
float slsl=60.0f; // filter sidelobe suppression level
liquid_float_complex x, y;
firhilbf firR2C = firhilbf_create(m,slsl);
firhilbf firC2R = firhilbf_create(m,slsl);
nco_crcf nco_shift = nco_crcf_create(LIQUID_NCO);
float shift_freq = 0;
agc = agc_crcf_create(); agc = agc_crcf_create();
agc_crcf_set_bandwidth(agc, 1e-3f); agc_crcf_set_bandwidth(agc, 1e-3f);
@ -106,19 +116,20 @@ void DemodulatorThread::threadMain() {
freqdem_demodulate_block(fdem, &agc_data[0], num_written, &demod_output[0]); freqdem_demodulate_block(fdem, &agc_data[0], num_written, &demod_output[0]);
if (stereo) { if (stereo) {
int shift_freq = 38000 - inp->bandwidth;
double freq = (2.0 * M_PI) * (((double) abs(shift_freq)) / ((double) inp->bandwidth)); double freq = (2.0 * M_PI) * (((float) abs(38000)) / ((float) inp->bandwidth));
if (shift_freq != freq) {
nco_crcf_set_frequency(nco_shift, freq);
shift_freq = freq;
}
for (int i = 0; i < num_written; i++) { for (int i = 0; i < num_written; i++) {
freq_index += freq; firhilbf_r2c_execute(firR2C,demod_output[i],&x);
nco_crcf_mix_down(nco_shift, x, &y);
demod_output_stereo[i] = demod_output[i] * sin(freq_index); // + demod_output[i] * cos(freq_index); nco_crcf_step(nco_shift);
while (freq_index > (M_PI * 2.0)) { firhilbf_c2r_execute(firR2C,y,&demod_output_stereo[i]);
freq_index -= (M_PI * 2.0);
}
while (freq_index < (M_PI * 2.0)) {
freq_index += (M_PI * 2.0);
}
} }
} }
@ -247,6 +258,9 @@ void DemodulatorThread::threadMain() {
} }
agc_crcf_destroy(agc); agc_crcf_destroy(agc);
firhilbf_destroy(firR2C);
firhilbf_destroy(firC2R);
nco_crcf_destroy(nco_shift);
while (!buffers.empty()) { while (!buffers.empty()) {
AudioThreadInput *audioDataDel = buffers.front(); AudioThreadInput *audioDataDel = buffers.front();