New AFSK demodulators.

'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.

Author: wb2osz

src/atest.c

@@ -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;	
@@ -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;
@@ -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;
@@ -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;

src/config.c

@@ -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;

src/demod.c

@@ -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 */
@@ -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;
 		}
 	      }

src/demod_9600.c

@@ -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. */