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authorKyle Keen <keenerd@gmail.com>2012-05-29 13:02:36 -0400
committerSteve Markgraf <steve@steve-m.de>2012-07-17 20:42:03 +0200
commit37f5559d1c21421241a9b1d791e297edfd462d36 (patch)
tree7ad6e5fb76a62df8c33db469e528105cc08ca175 /src/rtl_fm.c
parentfc390b32247e954cedcb6ff1fac580e768016014 (diff)
rtl_fm: satisfactory squelch
Signed-off-by: Steve Markgraf <steve@steve-m.de>
Diffstat (limited to 'src/rtl_fm.c')
-rw-r--r--src/rtl_fm.c54
1 files changed, 44 insertions, 10 deletions
diff --git a/src/rtl_fm.c b/src/rtl_fm.c
index 5b6e9e4..1110cb1 100644
--- a/src/rtl_fm.c
+++ b/src/rtl_fm.c
@@ -26,8 +26,7 @@
* replace atan2 with a fast approximation
* in-place array operations
* wide band support
- * squelch
- * better threading
+ * refactor to look like rtl_tcp
*/
#include <errno.h>
@@ -63,6 +62,7 @@ struct fm_state
int prev_index;
int downsample; /* min 4, max 256 */
int output_scale;
+ int squelch_level;
int signal[2048]; /* 16 bit signed i/q pairs */
int16_t signal2[2048]; /* signal has lowpass, signal2 has demod */
int signal_len;
@@ -82,6 +82,7 @@ void usage(void)
"\t[-s samplerate (default: 24000 Hz)]\n"
"\t[-d device_index (default: 0)]\n"
"\t[-g tuner_gain (default: -1dB)]\n"
+ "\t[-l squelch_level (default: 150)]\n"
"\tfilename (a '-' dumps samples to stdout)\n\n"
"Produces signed 16 bit ints, use sox to hear them.\n"
"\trtl_fm ... | play -t raw -r 24k -e signed-integer -b 16 -c 1 -\n\n");
@@ -116,9 +117,8 @@ void rotate_90(unsigned char *buf, uint32_t len)
{
uint32_t i;
unsigned char tmp;
- for (i=0; i<len; i+=8)
- {
- /* uint_8 negation = 255 - x */
+ for (i=0; i<len; i+=8) {
+ /* uint8_t negation = 255 - x */
tmp = 255 - buf[i+3];
buf[i+3] = buf[i+2];
buf[i+2] = tmp;
@@ -168,9 +168,6 @@ int polar_discriminant(int ar, int aj, int br, int bj)
int cr, cj;
double angle;
multiply(ar, aj, br, -bj, &cr, &cj);
- /* fake squelch */
- //if (abs(cr) + abs(cj) < 50000)
- // {return 0;}
angle = atan2((double)cj, (double)cr);
return (int)(angle / 3.14159 * (1<<14));
}
@@ -190,16 +187,49 @@ void fm_demod(struct fm_state *fm)
fm->pre_j = fm->signal[fm->signal_len - 1];
}
+int mad(int *samples, int len, int step)
+/* mean average deviation */
+{
+ int i=0, sum=0, ave=0;
+ for (i=0; i<len; i+=step) {
+ sum += samples[i];
+ }
+ ave = sum / (len * step);
+ sum = 0;
+ for (i=0; i<len; i+=step) {
+ sum += abs(samples[i] - ave);
+ }
+ return sum / (len * step);
+}
+
+void post_squelch(struct fm_state *fm)
+{
+ int i, i2, dev_r, dev_j, len, sq_l;
+ /* only for small samples, big samples need chunk processing */
+ len = fm->signal_len;
+ sq_l = fm->squelch_level;
+ dev_r = mad(&(fm->signal[0]), len, 2);
+ dev_j = mad(&(fm->signal[1]), len, 2);
+ if ((dev_r > sq_l) || (dev_j > sq_l)) {
+ return;
+ }
+ /* weak signal, kill it entirely */
+ for (i=0; i<len; i++) {
+ fm->signal2[i/2] = 0;
+ }
+}
+
static void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx)
{
struct fm_state *fm2;
if (!ctx) {
return;
}
- fm2 = (struct fm_struct*)(ctx); // bad conversion?
+ fm2 = (struct fm_struct*)(ctx); // warning?
rotate_90(buf, len);
low_pass(fm2, buf, len);
fm_demod(fm2);
+ post_squelch(fm2);
/* ignore under runs for now */
fwrite(fm2->signal2, 2, fm2->signal_len/2, fm2->file);
}
@@ -246,8 +276,9 @@ int main(int argc, char **argv)
uint32_t out_block_size = DEFAULT_BUF_LENGTH;
int device_count;
char vendor[256], product[256], serial[256];
+ fm.squelch_level = 150;
#ifndef _WIN32
- while ((opt = getopt(argc, argv, "d:f:g:s:b:S::")) != -1) {
+ while ((opt = getopt(argc, argv, "d:f:g:s:b:l:S::")) != -1) {
switch (opt) {
case 'd':
dev_index = atoi(optarg);
@@ -258,6 +289,9 @@ int main(int argc, char **argv)
case 'g':
gain = (int)(atof(optarg) * 10);
break;
+ case 'l':
+ fm.squelch_level = (int)atof(optarg);
+ break;
case 's':
samp_rate = (uint32_t)atof(optarg);
break;