ModemKit *ModemFMStereo::buildKit(long long sampleRate, int audioSampleRate) {
ModemKitFMStereo *kit = new ModemKitFMStereo;
kit->audioResampleRatio = double(audioSampleRate) / double(sampleRate);
kit->sampleRate = sampleRate;
kit->audioSampleRate = audioSampleRate;
float As = 60.0f; // stop-band attenuation [dB]
kit->audioResampler = msresamp_rrrf_create(kit->audioResampleRatio, As);
kit->stereoResampler = msresamp_rrrf_create(kit->audioResampleRatio, As);
// Stereo filters / shifters
double firStereoCutoff = 16000.0 / double(audioSampleRate);
// filter transition
float ft = 1000.0f / double(audioSampleRate);
// fractional timing offset
float mu = 0.0f;
if (firStereoCutoff < 0) {
firStereoCutoff = 0;
}
if (firStereoCutoff > 0.5) {
firStereoCutoff = 0.5;
}
unsigned int h_len = estimate_req_filter_len(ft, As);
float *h = new float[h_len];
liquid_firdes_kaiser(h_len, firStereoCutoff, As, mu, h);
kit->firStereoLeft = firfilt_rrrf_create(h, h_len);
kit->firStereoRight = firfilt_rrrf_create(h, h_len);
// stereo pilot filter
float bw = float(sampleRate);
if (bw < 100000.0) {
bw = 100000.0;
}
unsigned int order = 5; // filter order
float f0 = ((float) 19000 / bw);
float fc = ((float) 19500 / bw);
float Ap = 1.0f;
kit->iirStereoPilot = iirfilt_crcf_create_prototype(LIQUID_IIRDES_CHEBY2, LIQUID_IIRDES_BANDPASS, LIQUID_IIRDES_SOS, order, fc, f0, Ap, As);
kit->firStereoR2C = firhilbf_create(5, 60.0f);
kit->firStereoC2R = firhilbf_create(5, 60.0f);
kit->stereoPilot = nco_crcf_create(LIQUID_VCO);
nco_crcf_reset(kit->stereoPilot);
nco_crcf_pll_set_bandwidth(kit->stereoPilot, 0.25f);
return kit;
}
int main() {
unsigned int m=5; // filter semi-length
float slsl=60.0f; // filter sidelobe suppression level
// create Hilbert transform objects
firhilbf q0 = firhilbf_create(m,slsl);
firhilbf q1 = firhilbf_create(m,slsl);
float complex x; // interpolator input
float y[2]; // interpolator output
float complex z; // decimator output
// ...
// execute transforms
firhilbf_interp_execute(q0, x, y); // interpolator
firhilbf_decim_execute(q1, y, &z); // decimator
// clean up allocated memory
firhilbf_destroy(q0);
firhilbf_destroy(q1);
}
// create ampmodem object
// _m : modulation index
// _fc : carrier frequency
// _type : AM type (e.g. LIQUID_AMPMODEM_DSB)
// _suppressed_carrier : carrier suppression flag
ampmodem ampmodem_create(float _m,
float _fc,
liquid_ampmodem_type _type,
int _suppressed_carrier)
{
ampmodem q = (ampmodem) malloc(sizeof(struct ampmodem_s));
q->type = _type;
q->m = _m;
q->fc = _fc;
q->suppressed_carrier = (_suppressed_carrier == 0) ? 0 : 1;
// create nco, pll objects
q->oscillator = nco_crcf_create(LIQUID_NCO);
nco_crcf_set_frequency(q->oscillator, 2*M_PI*q->fc);
nco_crcf_pll_set_bandwidth(q->oscillator,0.05f);
// suppressed carrier
q->ssb_alpha = 0.01f;
q->ssb_q_hat = 0.0f;
// single side-band
q->hilbert = firhilbf_create(9, 60.0f);
// double side-band
ampmodem_reset(q);
// debugging
#if DEBUG_AMPMODEM
q->debug_x = windowcf_create(DEBUG_AMPMODEM_BUFFER_LEN);
q->debug_phase_error = windowf_create(DEBUG_AMPMODEM_BUFFER_LEN);
q->debug_freq_error = windowf_create(DEBUG_AMPMODEM_BUFFER_LEN);
#endif
return q;
}
int main() {
unsigned int m=5; // Hilbert filter semi-length
float As=60.0f; // stop-band attenuation [dB]
float fc=0.37f; // signal center frequency
unsigned int num_samples=128; // number of samples
// data arrays
float complex x[num_samples]; // complex input
float y[2*num_samples]; // real output
// initialize input array
unsigned int i;
for (i=0; i<num_samples; i++)
x[i] = cexpf(_Complex_I*2*M_PI*fc*i);
// create Hilbert transform object
firhilbf q = firhilbf_create(m,As);
// execute transform (interpolator) to compute real signal
firhilbf_interp_execute_block(q, x, num_samples, y);
// destroy Hilbert transform object
firhilbf_destroy(q);
printf("firhilb interpolated %u complex samples to %u real samples\n",
2*num_samples, num_samples);
//
// export results to file
//
FILE*fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
fprintf(fid,"h_len=%u;\n", 4*m+1);
fprintf(fid,"num_samples=%u;\n", num_samples);
for (i=0; i<num_samples; i++) {
// print results
fprintf(fid,"x(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%3u) = %12.4e;\n", 2*i+1, y[2*i+0]);
fprintf(fid,"y(%3u) = %12.4e;\n", 2*i+2, y[2*i+1]);
}
// plot results
fprintf(fid,"nfft=512;\n");
fprintf(fid,"%% compute normalized windowing functions\n");
fprintf(fid,"wx = 1.8534/num_samples*hamming(length(x)).'; %% x window\n");
fprintf(fid,"wy = 1.8534/num_samples*hamming(length(y)).'; %% y window\n");
fprintf(fid,"X=20*log10(abs( (fft(x.*wx,nfft))));\n");
fprintf(fid,"Y=20*log10(abs(fftshift(fft(y.*wy,nfft))));\n");
fprintf(fid,"f =[0:(nfft-1)]/nfft-0.5;\n");
fprintf(fid,"fi=[0:(nfft-1)]/(2*nfft);\n");
fprintf(fid,"figure; plot(fi,X,'Color',[0.5 0.5 0.5],f,Y,'LineWidth',2);\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"axis([-0.5 0.5 -80 20]);\n");
fprintf(fid,"xlabel('normalized frequency');\n");
fprintf(fid,"ylabel('PSD [dB]');\n");
fprintf(fid,"legend('original/complex','transformed/interpolated','location','northeast');");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
int main() {
unsigned int m=5; // Hilbert filter semi-length
float As=60.0f; // stop-band attenuation [dB]
float fc=0.37f; // signal center frequency
unsigned int num_samples=64; // number of samples
// derived values
unsigned int h_len = 4*m+1;
unsigned int N = num_samples + h_len;
// create Hilbert transform object
firhilbf q = firhilbf_create(m,As);
firhilbf_print(q);
// data arrays
float x[N]; // real input
float complex y[N]; // complex output
float z[N]; // real output
// initialize input array
unsigned int i;
for (i=0; i<N; i++) {
x[i] = cosf(2*M_PI*fc*i);
x[i] *= (i < num_samples) ? 1.855f*hamming(i,num_samples) : 0.0f;
}
for (i=0; i<N; i++) {
// execute real-to-complex conversion
firhilbf_r2c_execute(q, x[i], &y[i]);
// execute complex-to-real conversion
firhilbf_c2r_execute(q, y[i], &z[i]);
//printf("y(%3u) = %12.8f + j*%12.8f;\n", i+1, crealf(y[i]), cimagf(y[i]));
}
// destroy Hilbert transform object
firhilbf_destroy(q);
//
// export results to file
//
FILE*fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
fprintf(fid,"h_len=%u;\n", 4*m+1);
fprintf(fid,"num_samples=%u;\n", num_samples);
fprintf(fid,"N=%u;\n", N);
fprintf(fid,"t = 0:(N-1);\n");
for (i=0; i<N; i++) {
// print results
fprintf(fid,"x(%3u) = %12.4e;\n", i+1, x[i]);
fprintf(fid,"y(%3u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
fprintf(fid,"z(%3u) = %12.4e;\n", i+1, z[i]);
}
fprintf(fid,"figure;\n");
fprintf(fid," subplot(3,1,1); plot(t,x);\n");
fprintf(fid," subplot(3,1,2); plot(t,real(y), t,imag(y));\n");
fprintf(fid," subplot(3,1,3); plot(t,z);\n");
// plot results
fprintf(fid,"nfft=512;\n");
fprintf(fid,"%% compute normalized windowing functions\n");
fprintf(fid,"X=20*log10(abs(fftshift(fft(x/num_samples,nfft))));\n");
fprintf(fid,"Y=20*log10(abs(fftshift(fft(y/num_samples,nfft))));\n");
fprintf(fid,"Z=20*log10(abs(fftshift(fft(z/num_samples,nfft))));\n");
fprintf(fid,"f =[0:(nfft-1)]/nfft-0.5;\n");
fprintf(fid,"figure; plot(f,X,'LineWidth',1,'Color',[0.50 0.50 0.50],...\n");
fprintf(fid," f,Y,'LineWidth',2,'Color',[0.00 0.50 0.25],...\n");
fprintf(fid," f,Z,'LineWidth',1,'Color',[0.00 0.25 0.50]);\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"axis([-0.5 0.5 -80 20]);\n");
fprintf(fid,"xlabel('normalized frequency');\n");
fprintf(fid,"ylabel('PSD [dB]');\n");
fprintf(fid,"legend('original/real','transformed/complex','regenerated/real',1);");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
