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New AFSK demodulators.
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'A' uses mark and space filters but simpler and cleaner
than earlier attempts.
New 'B' uses a different technique where the demodulated
signal is proportional to the frequency.
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@wb2osz
wb2osz committed Nov 28, 2020
1 parent fdf660a commit 9922f17
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Showing 12 changed files with 754 additions and 584 deletions.
18 changes: 10 additions & 8 deletions src/atest.c
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Original file line number Diff line number Diff line change
Expand Up @@ -236,7 +236,7 @@ int main (int argc, char *argv[])
my_audio_config.achan[channel].space_freq = DEFAULT_SPACE_FREQ;
my_audio_config.achan[channel].baud = DEFAULT_BAUD;

strlcpy (my_audio_config.achan[channel].profiles, "E", sizeof(my_audio_config.achan[channel].profiles));
strlcpy (my_audio_config.achan[channel].profiles, "A", sizeof(my_audio_config.achan[channel].profiles));

my_audio_config.achan[channel].num_freq = 1;
my_audio_config.achan[channel].offset = 0;
Expand Down Expand Up @@ -430,19 +430,21 @@ int main (int argc, char *argv[])
/* We have similar logic in direwolf.c, config.c, gen_packets.c, and atest.c, */
/* that need to be kept in sync. Maybe it could be a common function someday. */

if (my_audio_config.achan[0].baud == 100) {
if (my_audio_config.achan[0].baud == 100) { // What was this for?
my_audio_config.achan[0].modem_type = MODEM_AFSK;
my_audio_config.achan[0].mark_freq = 1615;
my_audio_config.achan[0].space_freq = 1785;
strlcpy (my_audio_config.achan[0].profiles, "D", sizeof(my_audio_config.achan[0].profiles));
//strlcpy (my_audio_config.achan[0].profiles, "A", sizeof(my_audio_config.achan[0].profiles));
}
else if (my_audio_config.achan[0].baud < 600) {
else if (my_audio_config.achan[0].baud < 600) { // e.g. HF SSB packet
my_audio_config.achan[0].modem_type = MODEM_AFSK;
my_audio_config.achan[0].mark_freq = 1600;
my_audio_config.achan[0].space_freq = 1800;
strlcpy (my_audio_config.achan[0].profiles, "D", sizeof(my_audio_config.achan[0].profiles));
// Previously we had a "D" which was fine tuned for 300 bps.
// In v1.7, it's not clear if we should use "B" or just stick with "A".
//strlcpy (my_audio_config.achan[0].profiles, "B", sizeof(my_audio_config.achan[0].profiles));
}
else if (my_audio_config.achan[0].baud < 1800) {
else if (my_audio_config.achan[0].baud < 1800) { // common 1200
my_audio_config.achan[0].modem_type = MODEM_AFSK;
my_audio_config.achan[0].mark_freq = DEFAULT_MARK_FREQ;
my_audio_config.achan[0].space_freq = DEFAULT_SPACE_FREQ;
Expand All @@ -460,7 +462,7 @@ int main (int argc, char *argv[])
my_audio_config.achan[0].space_freq = 0;
strlcpy (my_audio_config.achan[0].profiles, "", sizeof(my_audio_config.achan[0].profiles));
}
else if (my_audio_config.achan[0].baud == 12345) {
else if (my_audio_config.achan[0].baud == 12345) { // Hack for different use of 9600
my_audio_config.achan[0].modem_type = MODEM_AIS;
my_audio_config.achan[0].baud = 9600;
my_audio_config.achan[0].mark_freq = 0;
Expand All @@ -473,7 +475,7 @@ int main (int argc, char *argv[])
// Will make more precise in afsk demod init.
my_audio_config.achan[0].mark_freq = 2083; // Actually 2083.3 - logic 1.
my_audio_config.achan[0].space_freq = 1563; // Actually 1562.5 - logic 0.
strlcpy (my_audio_config.achan[0].profiles, "D", sizeof(my_audio_config.achan[0].profiles));
strlcpy (my_audio_config.achan[0].profiles, "A", sizeof(my_audio_config.achan[0].profiles));
}
else {
my_audio_config.achan[0].modem_type = MODEM_SCRAMBLE;
Expand Down
2 changes: 1 addition & 1 deletion src/config.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1337,7 +1337,7 @@ void config_init (char *fname, struct audio_s *p_audio_config,
// Will make more precise in afsk demod init.
p_audio_config->achan[channel].mark_freq = 2083; // Actually 2083.3 - logic 1.
p_audio_config->achan[channel].space_freq = 1563; // Actually 1562.5 - logic 0.
// ? strlcpy (p_audio_config->achan[channel].profiles, "D", sizeof(p_audio_config->achan[channel].profiles));
// ? strlcpy (p_audio_config->achan[channel].profiles, "A", sizeof(p_audio_config->achan[channel].profiles));
}
else {
p_audio_config->achan[channel].modem_type = MODEM_SCRAMBLE;
Expand Down
67 changes: 39 additions & 28 deletions src/demod.c
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Original file line number Diff line number Diff line change
Expand Up @@ -198,46 +198,57 @@ int demod_init (struct audio_s *pa)
assert (num_letters == (int)(strlen(just_letters)));

/*
* Pick a good default demodulator if none specified.
* Pick a good default demodulator if none specified.
* Previously, we had "D" optimized for 300 bps.
* Gone in 1.7 so it is always "A+".
*/
if (num_letters == 0) {
strlcpy (just_letters, "A", sizeof(just_letters));
num_letters = strlen(just_letters);

if (save_audio_config_p->achan[chan].baud < 600) {

/* This has been optimized for 300 baud. */

strlcpy (just_letters, "D", sizeof(just_letters));
if (have_plus != -1) have_plus = 1; // Add as default for version 1.2
// If not explicitly turned off.
}

}
else {
/*
* Special case for ARM.
* The higher end ARM chips have loads of power but many people
* are using a single core Pi Zero or similar.
* (I'm still using a model 1 for my digipeater/IGate!)
* Decreasing CPU requirement has a negligible impact on decoding performance.
*
* atest -PA- 01_Track_1.wav --> 1002 packets decoded.
* atest -PA- -D3 01_Track_1.wav --> 997 packets decoded.
*
* Someone concerned about 1/2 of one percent difference can add "-D 1"
*/
#if __arm__
/* We probably don't have a lot of CPU power available. */
/* Previously we would use F if possible otherwise fall back to A. */

/* In version 1.2, new default is E+ /3. */
strlcpy (just_letters, "E", sizeof(just_letters)); // version 1.2 now E.
if (have_plus != -1) have_plus = 1; // Add as default for version 1.2
// If not explicitly turned off.
if (save_audio_config_p->achan[chan].decimate == 0) {
if (save_audio_config_p->adev[ACHAN2ADEV(chan)].samples_per_sec > 40000) {
save_audio_config_p->achan[chan].decimate = 3;
}
}
#else
strlcpy (just_letters, "E", sizeof(just_letters)); // version 1.2 changed C to E.
if (have_plus != -1) have_plus = 1; // Add as default for version 1.2
// If not explicitly turned off.
#endif
if (save_audio_config_p->achan[chan].decimate == 0) {
if (save_audio_config_p->adev[ACHAN2ADEV(chan)].samples_per_sec > 40000) {
save_audio_config_p->achan[chan].decimate = 3;
}
num_letters = 1;
}
#endif

/*
* Number of filter taps is proportional to number of audio samples in a "symbol" duration.
* These can get extremely large for low speeds, e.g. 300 baud.
* In this case, increase the decimation ration. Crude approximation. Could be improved.
*/
if (save_audio_config_p->achan[chan].decimate == 0 &&
save_audio_config_p->adev[ACHAN2ADEV(chan)].samples_per_sec > 40000 &&
save_audio_config_p->achan[chan].baud < 600) {

// Avoid enormous number of filter taps.

save_audio_config_p->achan[chan].decimate = 3;
}

assert (num_letters == (int)(strlen(just_letters)));

/*
* Put it back together again.
*/
assert (num_letters == (int)(strlen(just_letters)));

/* At this point, have_plus can have 3 values: */
/* 1 = turned on, either explicitly or by applied default */
Expand Down Expand Up @@ -286,7 +297,7 @@ int demod_init (struct audio_s *pa)

if (save_audio_config_p->achan[chan].decimate == 0) {
save_audio_config_p->achan[chan].decimate = 1;
if (strchr (just_letters, 'D') != NULL && save_audio_config_p->adev[ACHAN2ADEV(chan)].samples_per_sec > 40000) {
if (strchr (just_letters, 'B') != NULL && save_audio_config_p->adev[ACHAN2ADEV(chan)].samples_per_sec > 40000) {
save_audio_config_p->achan[chan].decimate = 3;
}
}
Expand Down
2 changes: 1 addition & 1 deletion src/demod_9600.c
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Original file line number Diff line number Diff line change
Expand Up @@ -221,7 +221,7 @@ void demod_9600_init (enum modem_t modem_type, int samples_per_sec, int baud, st

//dw_printf ("demod_9600_init: call gen_lowpass(fc=%.2f, , size=%d, )\n", fc, D->lp_filter_size);

(void)gen_lowpass (fc, D->lp_filter, D->lp_filter_size, D->lp_window, 0);
gen_lowpass (fc, D->lp_filter, D->lp_filter_size, D->lp_window);

/* Version 1.2: Experiment with different slicing levels. */

Expand Down
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