@@ -956,6 +956,15 @@ for debuging.
@item kbd_alpha
Kaiser Bessel derived window parameter
+@item am_threshold
+AM station detection threshold
+
+@item fm_threshold
+FM station detection threshold, a lower value allows detection of weaker stations but
+it can also result in the detection of SDR artifacts such as reflections of strong FM stations
+as weak stations. Future versions may be better able to separate weak stations from artifacts
+looking like weak stations.
+
@item am_mode
AM Demodulation method. Several different methods are supported.
@table @samp
@@ -152,6 +152,9 @@ typedef struct SDRContext {
int emphasis_mode;
int am_fft_ref;
+ float am_threshold;
+ float fm_threshold;
+
pthread_t hw_thread;
int thread_started;
pthread_mutex_t mutex; ///< Mutex to protect common variable between mainthread and hw_thread, and also to protect soapy from concurrent calls
@@ -64,17 +64,9 @@
#define STATION_TIMEOUT 100 ///< The number of frames after which a station is removed if it was not detected
#define CANDIDATE_STATION_TIMEOUT 4
-/*
- * 100 detects nothing
- * 50 detects a good bit but not all
- */
-#define AM_THRESHOLD 20
-
#define AM_MAX23 0.06 //smaller causes failure on synthetic signals
#define AM_MAX4 0.02
-#define FM_THRESHOLD 50 //TODO adjust
-
//Least squares fit at 1khz points of frequency response shown by Frank McClatchie, FM SYSTEMS, INC. 800-235-6960
static double emphasis75us(int f)
{
@@ -529,7 +521,7 @@ static int probe_am(SDRContext *sdr)
continue;
//TODO also check for symmetry in the spectrum
- if (mid > 0 && score > AM_THRESHOLD &&
+ if (mid > 0 && score > sdr->am_threshold &&
sdr->len2block[i - 1] < mid && sdr->len2block[i + 1] <= mid &&
sdr->len2block[i - 2] < mid*AM_MAX23 && sdr->len2block[i + 2] < mid*AM_MAX23 &&
sdr->len2block[i - 3] < mid*AM_MAX23 && sdr->len2block[i + 3] < mid*AM_MAX23
@@ -583,7 +575,7 @@ static double find_am_carrier(SDRContext *sdr, const AVComplexFloat *data, int d
avg += len2block[i + index];
score = len * mid / (avg - mid);
//find optimal frequency for this block if we have a carrier
- if (score > AM_THRESHOLD / 4) {
+ if (score > sdr->am_threshold / 4) {
double peak_i = find_peak_macleod(sdr, data, i_max, data_len, NULL);
if (peak_i < 0)
return peak_i;
@@ -858,7 +850,7 @@ static int probe_fm(SDRContext *sdr)
if (last_score[1] >= last_score[0] &&
last_score[1] > last_score[2] &&
- last_score[1] > FM_THRESHOLD) {
+ last_score[1] > sdr->fm_threshold) {
float rmax = max_in_range(sdr, i-half_bw_i/4, i+half_bw_i/4);
int lowcount = countbelow(sdr, i-half_bw_i/4, i+half_bw_i/4, rmax / 100);
@@ -2122,6 +2114,10 @@ const AVOption avpriv_sdr_options[] = {
{ "emphasis75us", "FM De-Emphasis 75us", 0, AV_OPT_TYPE_CONST, {.i64 = EMPHASIS_75us}, 0, 0, DEC, "fm_emphasis"},
{ "emphasis50us", "FM De-Emphasis 50us", 0, AV_OPT_TYPE_CONST, {.i64 = EMPHASIS_50us}, 0, 0, DEC, "fm_emphasis"},
{ "none" , "No FM De-Emphasis" , 0, AV_OPT_TYPE_CONST, {.i64 = EMPHASIS_NONE}, 0, 0, DEC, "fm_emphasis"},
+
+ { "am_threshold" , "AM detection threshold", OFFSET(am_threshold), AV_OPT_TYPE_FLOAT, {.dbl = 20}, 0, FLT_MAX, DEC},
+ { "fm_threshold" , "FM detection threshold", OFFSET(fm_threshold), AV_OPT_TYPE_FLOAT, {.dbl = 50}, 0, FLT_MAX, DEC},
+
{ NULL },
};
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- doc/demuxers.texi | 9 +++++++++ libavradio/sdr.h | 3 +++ libavradio/sdrdemux.c | 18 +++++++----------- 3 files changed, 19 insertions(+), 11 deletions(-)