kopia lustrzana https://github.com/F5OEO/PiFmRds
Functional rds_wav that generates stereo multiplex signals
Christophe Jacquet
rodzic
e1defb48e6
commit
e758ee63a0
201
src/fm_mpx.c
201
src/fm_mpx.c
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@ -19,10 +19,14 @@
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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fm_mpx.c: generates an FM multiplex signal containing RDS plus possibly
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monaural or stereo audio.
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*/
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#include <sndfile.h>
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#include <stdlib.h>
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#include <strings.h>
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#include <math.h>
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#include "rds.h"
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@ -34,8 +38,8 @@
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#define FIR_HALF_SIZE 30
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#define FIR_SIZE (2*FIR_HALF_SIZE-1)
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#define LENGTH 114000
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// TODO: remove constant
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size_t length;
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// coefficients of the low-pass FIR filter
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float low_pass_fir[FIR_HALF_SIZE];
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@ -52,81 +56,112 @@ int phase_19 = 0;
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float downsample_factor;
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float rds_buffer[LENGTH] = {0};
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float audio_buffer[LENGTH] = {0};
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float *audio_buffer;
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int audio_index = 0;
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int audio_len = 0;
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float audio_pos;
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float out = 0;
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float alpha = .03;
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float fir_buffer[FIR_SIZE] = {0};
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float fir_buffer_mono[FIR_SIZE] = {0};
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float fir_buffer_stereo[FIR_SIZE] = {0};
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int fir_index = 0;
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int channels;
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SNDFILE *inf;
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float *alloc_empty_buffer(size_t length) {
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float *p = malloc(length * sizeof(float));
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if(p == NULL) return NULL;
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bzero(p, length * sizeof(float));
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return p;
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}
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int fm_mpx_open(char *filename) {
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// Open the input file
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SF_INFO sfinfo;
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if(! (inf = sf_open(filename, SFM_READ, &sfinfo))) {
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fprintf(stderr, "Error: could not open input file %s.\n", filename) ;
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return EXIT_FAILURE; // TODO better error code
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}
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int in_samplerate = sfinfo.samplerate;
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downsample_factor = 228000. / in_samplerate;
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printf("Input: %d Hz, upsampling factor: %.2f\n", in_samplerate, downsample_factor);
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// Create the low-pass FIR filter
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float cutoff_freq = 15000 * .8;
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if(in_samplerate/2 < cutoff_freq) cutoff_freq = in_samplerate/2 * .8;
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low_pass_fir[FIR_HALF_SIZE-1] = 2 * cutoff_freq / 228000 /2;
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// Here we divide this coefficient by two because it will be counted twice
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// when applying the filter
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int fm_mpx_open(char *filename, size_t len) {
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length = len;
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// Only store half of the filter since it is symmetric
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for(int i=1; i<FIR_HALF_SIZE; i++) {
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low_pass_fir[FIR_HALF_SIZE-1-i] =
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sin(2 * PI * cutoff_freq * i / 228000) / (PI * i) // sinc
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* (.54 - .46 * cos(2*PI * (i+FIR_HALF_SIZE) / (2*FIR_HALF_SIZE)));
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// Hamming window
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if(filename != NULL) {
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// Open the input file
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SF_INFO sfinfo;
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if(! (inf = sf_open(filename, SFM_READ, &sfinfo))) {
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fprintf(stderr, "Error: could not open input file %s.\n", filename) ;
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return -1;
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}
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int in_samplerate = sfinfo.samplerate;
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downsample_factor = 228000. / in_samplerate;
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printf("Input: %d Hz, upsampling factor: %.2f\n", in_samplerate, downsample_factor);
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channels = sfinfo.channels;
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if(channels > 1) {
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printf("%d channels, generating stereo multiplex.\n", channels);
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} else {
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printf("1 channel, monophonic operation.\n");
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}
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// Create the low-pass FIR filter
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float cutoff_freq = 15000 * .8;
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if(in_samplerate/2 < cutoff_freq) cutoff_freq = in_samplerate/2 * .8;
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low_pass_fir[FIR_HALF_SIZE-1] = 2 * cutoff_freq / 228000 /2;
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// Here we divide this coefficient by two because it will be counted twice
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// when applying the filter
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// Only store half of the filter since it is symmetric
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for(int i=1; i<FIR_HALF_SIZE; i++) {
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low_pass_fir[FIR_HALF_SIZE-1-i] =
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sin(2 * PI * cutoff_freq * i / 228000) / (PI * i) // sinc
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* (.54 - .46 * cos(2*PI * (i+FIR_HALF_SIZE) / (2*FIR_HALF_SIZE)));
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// Hamming window
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}
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printf("Created low-pass FIR filter for audio channels, with cutoff at %.1f Hz\n", cutoff_freq);
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/*
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for(int i=0; i<FIR_HALF_SIZE; i++) {
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printf("%.5f ", low_pass_fir[i]);
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}
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printf("\n");
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*/
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audio_pos = downsample_factor;
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audio_buffer = alloc_empty_buffer(length * channels);
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if(audio_buffer == NULL) return -1;
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} // end if(filename != NULL)
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else {
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inf = NULL;
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// inf == NULL indicates that there is no audio
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}
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printf("Created low-pass FIR filter for audio channels, with cutoff at %.1f Hz\n", cutoff_freq);
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/*
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for(int i=0; i<FIR_HALF_SIZE; i++) {
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printf("%.5f ", low_pass_fir[i]);
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}
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printf("\n");
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*/
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audio_pos = downsample_factor;
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return 0; // TODO
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return 0;
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}
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int fm_mpx_get_samples(float *mpx_buffer) { // TODO accept length in argument
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get_rds_samples(rds_buffer, LENGTH);
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// samples provided by this function are in 0..10: they need to be divided by
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// 10 after.
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int fm_mpx_get_samples(float *mpx_buffer) {
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get_rds_samples(mpx_buffer, length);
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for(int i=0; i<LENGTH; i++) {
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if(inf == NULL) return 0; // if there is no audio, stop here
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for(int i=0; i<length; i++) {
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if(audio_pos >= downsample_factor) {
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audio_pos -= downsample_factor;
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if(audio_len == 0) {
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for(int j=0; j<2; j++) { // one retry
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audio_len = sf_read_float(inf, audio_buffer, LENGTH);
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audio_len = sf_read_float(inf, audio_buffer, length);
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if (audio_len < 0) {
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fprintf(stderr, "Error reading audio\n");
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exit(EXIT_FAILURE);
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return -1;
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}
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if(audio_len == 0) {
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sf_seek(inf, 0, SEEK_SET);
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@ -136,49 +171,72 @@ int fm_mpx_get_samples(float *mpx_buffer) { // TODO accept length in argument
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}
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audio_index = 0;
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} else {
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audio_index++;
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audio_len--;
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audio_index += channels;
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audio_len -= channels;
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}
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}
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// Apply FIR low-pass filter
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fir_buffer[fir_index] = audio_buffer[audio_index];
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// First store the current sample(s) into the FIR filter's ring buffer
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if(channels == 0) {
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fir_buffer_mono[fir_index] = audio_buffer[audio_index];
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} else {
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// In stereo operation, generate sum and difference signals
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fir_buffer_mono[fir_index] =
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audio_buffer[audio_index] + audio_buffer[audio_index+1];
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fir_buffer_stereo[fir_index] =
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audio_buffer[audio_index] - audio_buffer[audio_index+1];
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}
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fir_index++;
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if(fir_index >= FIR_SIZE) fir_index = 0;
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// Now apply the FIR low-pass filter
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/* As the FIR filter is symmetric, we do not multiply all
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the coefficients independently, but two-by-two, thus reducing
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the total number of multiplications by a factor of two
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*/
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out = 0;
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float out_mono = 0;
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float out_stereo = 0;
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int ifbi = fir_index; // ifbi = increasing FIR Buffer Index
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int dfbi = fir_index; // dfbi = decreasing FIR Buffer Index
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for(int fi=0; fi<FIR_HALF_SIZE; fi++) { // fi = Filter Index
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dfbi--;
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if(dfbi < 0) dfbi = FIR_SIZE-1;
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out += low_pass_fir[fi] * (fir_buffer[ifbi] + fir_buffer[dfbi]);
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out_mono +=
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low_pass_fir[fi] *
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(fir_buffer_mono[ifbi] + fir_buffer_mono[dfbi]);
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if(channels > 1) {
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out_stereo +=
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low_pass_fir[fi] *
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(fir_buffer_stereo[ifbi] + fir_buffer_stereo[dfbi]);
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}
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ifbi++;
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if(ifbi >= FIR_SIZE) ifbi = 0;
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}
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// End of FIR filter
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mpx_buffer[i] = (rds_buffer[i] +
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4*out /* +
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2 * carrier_38[phase_38] * out +
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.1*carrier_19[phase_19]*/) / 10;
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phase_19++;
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phase_38++;
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if(phase_19 >= 12) phase_19 = 0;
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if(phase_38 >= 6) phase_38 = 0;
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mpx_buffer[i] =
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mpx_buffer[i] + // RDS data samples are currently in mpx_buffer
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4.05*out_mono; // Unmodulated monophonic (or stereo-sum) signal
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if(channels>1) {
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mpx_buffer[i] +=
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4.05 * carrier_38[phase_38] * out_stereo + // Stereo difference signal
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.09*carrier_19[phase_19]; // Stereo pilot tone
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phase_19++;
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phase_38++;
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if(phase_19 >= 12) phase_19 = 0;
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if(phase_38 >= 6) phase_38 = 0;
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}
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audio_pos++;
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}
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return 0; // TODO
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return 0;
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}
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@ -186,5 +244,8 @@ int fm_mpx_close() {
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if(sf_close(inf) ) {
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fprintf(stderr, "Error closing audio file");
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}
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return 0; // TODO
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free(audio_buffer);
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return 0;
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}
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@ -21,6 +21,6 @@
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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extern int fm_mpx_open(char *filename);
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extern int fm_mpx_open(char *filename, size_t len);
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extern int fm_mpx_get_samples(float *mpx_buffer);
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extern int fm_mpx_close();
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@ -36,17 +36,20 @@
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/* Simple test program */
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int main(int argc, char **argv) {
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if(argc < 3) {
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if(argc < 4) {
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fprintf(stderr, "Error: missing argument.\n");
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fprintf(stderr, "Syntax: rds_wav <out.wav> <text>\n");
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fprintf(stderr, "Syntax: rds_wav <in_file> <out.wav> <text>\n");
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return EXIT_FAILURE;
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}
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set_rds_pi(0x1234);
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set_rds_ps(argv[2]);
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set_rds_rt(argv[2]);
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set_rds_ps(argv[3]);
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set_rds_rt(argv[3]);
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fm_mpx_open("sound_22050.wav");
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if(fm_mpx_open(argv[1], LENGTH) != 0) {
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printf("Could not setup FM mulitplex generator.\n");
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return EXIT_FAILURE;
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}
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@ -62,8 +65,8 @@ int main(int argc, char **argv) {
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sfinfo.seekable = 0;
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// Open the output file
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if (! (outf = sf_open(argv[1], SFM_WRITE, &sfinfo))) {
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fprintf(stderr, "Error: could not open output file %s.\n", argv[1]) ;
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if (! (outf = sf_open(argv[2], SFM_WRITE, &sfinfo))) {
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fprintf(stderr, "Error: could not open output file %s.\n", argv[2]) ;
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return EXIT_FAILURE;
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}
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@ -71,6 +74,11 @@ int main(int argc, char **argv) {
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for(int j=0; j<40; j++) {
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fm_mpx_get_samples(mpx_buffer);
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// scale samples
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for(int i=0; i<LENGTH; i++) {
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mpx_buffer[i] /= 10.;
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}
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if(sf_write_float(outf, mpx_buffer, LENGTH) != LENGTH) {
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fprintf(stderr, "Error: writing to file %s.\n", argv[1]);
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