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util/spkmodem-decode: separate silence check

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i conflated two separate tests in a previous change.

the silence check was defeated by still checking f
alongside it, which would be set, thus satisfying
the condition, and proceeding, which defeats the
purpose of the silence check (ignore false signal
that is actually noise) - so in the original patch
that i wrote, the extra checks actually do nothing.

this patch fixes that, and makes the logic a bit
clearer.

Signed-off-by: Leah Rowe <leah@libreboot.org>
This commit is contained in:
Leah Rowe
2026-03-12 23:26:47 +00:00
parent 4dc39990e1
commit 68fb740da2
1 changed files with 17 additions and 12 deletions
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util/spkmodem_decode/spkmodem-decode.c
+17 -12
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@@ -460,25 +460,30 @@ auto_detect_tone(struct decoder_state *st)
{
int f;
/*
* Don't also run auto-detect during decode,
* otherwise it would run for every sample.
*/
if (st->learn_samples >= LEARN_SAMPLES)
return;
/*
* Check both FIR windows.
* Inside separator frames, the separator window contains tone,
* during data frames the data window does; a minimum of
* the two captures the lowest active tone cluster more reliably.
* Ignore silence / near silence.
* Both FIR windows will be near zero when no signal exists.
*/
if (st->freq_data <= 2 && st->freq_separator <= 2) {
st->learn_samples++;
return;
}
/*
* Choose the lowest active tone.
* Separator frames carry tone in the separator window,
* data frames carry tone in the data window.
*/
f = st->freq_data;
if (st->freq_separator > 0 && st->freq_separator < f)
if (f <= 0 || (st->freq_separator > 0 &&
st->freq_separator < f))
f = st->freq_separator;
if (f > 0 || /* prevent noise from corrupting tone-learning */
st->freq_data > 2 || /* <--- stop from */
st->freq_separator > 2) { /* learning silence if no signal */
if (f > 0) {
if (f < st->freq_min)
st->freq_min = f;