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rtl_sdr_fm: make RMS squelch incremental and decimated

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This commit is contained in:
arancormonk
2025-09-03 15:17:07 -04:00
parent c6d3e4cea0
commit e700e418be
1 changed files with 51 additions and 16 deletions
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67
src/rtl_sdr_fm.cpp
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@@ -118,6 +118,11 @@ struct demod_state
int post_downsample;
int output_scale;
int squelch_level, conseq_squelch, squelch_hits, terminate_on_squelch;
/* Incremental, decimated RMS squelch estimator (power-domain, sqrt-free) */
int64_t squelch_running_power;
int squelch_decim_stride;
int squelch_decim_phase;
int squelch_window;
int downsample_passes;
int comp_fir_size;
int custom_atan;
@@ -689,23 +694,38 @@ void full_demod(struct demod_state *d)
}
/* power squelch (sqrt-free): compare mean power to squared threshold */
if (d->squelch_level) {
long int pwr = 0;
{
int j;
long p = 0L, t = 0L, s;
double dc, err;
for (j = 0; j < d->lp_len; j += 1) {
s = (long)d->lowpassed[j];
t += s;
p += s * s;
}
dc = (double)t; /* step is 1 */
err = t * 2 * dc - dc * dc * d->lp_len;
pwr = (long int)((p - err) / (d->lp_len ? d->lp_len : 1));
if (pwr < 0) pwr = 0;
/* Decimated block power estimate (no DC correction; EMA smooths) */
int stride = (d->squelch_decim_stride > 0) ? d->squelch_decim_stride : 16;
int phase = d->squelch_decim_phase;
int64_t p = 0;
int count = 0;
for (int j = phase; j < d->lp_len; j += stride) {
int64_t s2 = (int64_t)d->lowpassed[j];
p += s2 * s2;
count++;
}
long int thr2 = (long int)d->squelch_level * (long int)d->squelch_level;
if (pwr < thr2) {
/* Advance phase to sample different positions next block */
if (stride > 0) {
int adv = d->lp_len % stride;
d->squelch_decim_phase = (phase + adv) % stride;
}
if (count > 0) {
int64_t block_mean = p / count;
if (d->squelch_running_power == 0) {
/* Initialize on first measurement to avoid long ramp */
d->squelch_running_power = block_mean;
} else {
/* EMA: running += (block_mean - running) / window */
int w = (d->squelch_window > 0) ? d->squelch_window : 2048;
int shift = 0;
/* approximate log2(window), prefer power-of-two windows */
while ((1 << shift) < w && shift < 30) { shift++; }
int64_t delta = (block_mean - d->squelch_running_power);
d->squelch_running_power += (delta >> shift);
}
}
int64_t thr2 = (int64_t)d->squelch_level * (int64_t)d->squelch_level;
if (d->squelch_running_power < thr2) {
d->squelch_hits++;
for (i=0; i<d->lp_len; i++) {
d->lowpassed[i] = 0;
@@ -1041,6 +1061,11 @@ void demod_init_analog(struct demod_state *s)
s->now_lpr = 0;
s->dc_block = 1; //
s->dc_avg = 0;
/* Squelch estimator init */
s->squelch_running_power = 0;
s->squelch_decim_stride = 16; /* evaluate 1/16th samples for low CPU */
s->squelch_decim_phase = 0;
s->squelch_window = 2048; /* EMA window ~2048 samples */
/* Double-buffer init */
s->write_buf_index.store(0);
s->ready_buf_index.store(1);
@@ -1079,6 +1104,11 @@ void demod_init_ro2(struct demod_state *s)
s->now_lpr = 0;
s->dc_block = 1; //enabling by default, but offset tuning is also enabled, so center spike shouldn't be an issue
s->dc_avg = 0;
/* Squelch estimator init */
s->squelch_running_power = 0;
s->squelch_decim_stride = 16;
s->squelch_decim_phase = 0;
s->squelch_window = 2048;
/* Double-buffer init */
s->write_buf_index.store(0);
s->ready_buf_index.store(1);
@@ -1117,6 +1147,11 @@ void demod_init(struct demod_state *s)
s->now_lpr = 0;
s->dc_block = 1; //enabling by default, but offset tuning is also enabled, so center spike shouldn't be an issue
s->dc_avg = 0;
/* Squelch estimator init */
s->squelch_running_power = 0;
s->squelch_decim_stride = 16;
s->squelch_decim_phase = 0;
s->squelch_window = 2048;
/* Double-buffer init */
s->write_buf_index.store(0);
s->ready_buf_index.store(1);