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rtl_sdr: make RMS squelch sqrt-free

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This commit is contained in:
arancormonk
2025-09-03 14:48:33 -04:00
parent 03c6b28de3
commit cc200ea82c
1 changed files with 20 additions and 5 deletions
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25
src/rtl_sdr_fm.cpp
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@@ -671,7 +671,6 @@ long int rms(int16_t *samples, int len, int step)
void full_demod(struct demod_state *d)
{
int i, ds_p;
int sr = 0;
ds_p = d->downsample_passes;
if (ds_p) {
for (i=0; i < ds_p; i++) {
@@ -689,16 +688,32 @@ void full_demod(struct demod_state *d)
} else {
low_pass(d);
}
/* power squelch */
/* power squelch (sqrt-free): compare mean power to squared threshold */
if (d->squelch_level) {
sr = rms(d->lowpassed, d->lp_len, 1);
if (sr < 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;
}
long int thr2 = (long int)d->squelch_level * (long int)d->squelch_level;
if (pwr < thr2) {
d->squelch_hits++;
for (i=0; i<d->lp_len; i++) {
d->lowpassed[i] = 0;
}
} else {
d->squelch_hits = 0;}
d->squelch_hits = 0;
}
}
d->mode_demod(d); /* lowpassed -> result */
if (d->mode_demod == &raw_demod) {