Version 20220313-1: roll back FM AFC code with unwanted pop noise

CHANGES.md

@@ -28,6 +28,7 @@
 
 ## Changes (including requirement changes)
 
+* 20220313-1: Removed experimental FM AFC code due to periodical noise generation. `-A` option is removed as well.
 * 20220313-0: Moved FineTuner object into independent files. Added experimental 10Hz-step IF AFC for FM broadcast (use `-A` option to enable). Simplified INSTALL-latest-libvolk.md.
 * 20220221-0: Shortened polling periods for Airspy R2/Mini and Airspy HF+ from 1 second to 100 milliseconds. Also reduced AGC output levels for CW and WSPR to prevent output overdrive.
 * 20220206-0: Rolled back the workaround of exit(0) in 20220205-1, because this is no longer necessary when a proper fix is done on Airspy HF+ driver.

README.md

@@ -2,7 +2,7 @@
 
 # airspy-fmradion
 
-* Version 20220313-0
+* Version 20220313-1
 * For MacOS (both Intel and Apple Silicon) and Linux
 
 ## Contributing
@@ -200,7 +200,6 @@ Compile and install
  - `-l dB` Enable IF squelch, set the level to minus given value of dB
  - `-E stages` Enable multipath filter for FM (For stable reception only: turn off if reception becomes unstable)
  - `-r ppm` Set IF offset in ppm (range: +-1000000ppm) (Note: this option affects output pitch and timing: *use for the output timing compensation only!*
- - `-A` (For FM only) Experimental 10Hz-step IF AFC
 
 ## Major changes
 

main.cpp

@@ -51,7 +51,7 @@
 // define this for enabling coefficient monitor functions
 // #undef COEFF_MONITOR
 
-#define AIRSPY_FMRADION_VERSION "20220313-0"
+#define AIRSPY_FMRADION_VERSION "20220313-1"
 
 // Flag to set graceful termination
 // in process_signals()
@@ -156,7 +156,6 @@ void usage() {
       "  -r ppm         Set IF offset in ppm (range: +-1000000ppm)\n"
       "                 (This option affects output pitch and timing:\n"
       "                  use for the output timing compensation only!)\n"
-      "  -A             (FM only) experimental 10Hz-step IF AFC\n"
       "\n"
       "Configuration options for RTL-SDR devices\n"
       "  freq=<int>     Frequency of radio station in Hz (default 100000000)\n"
@@ -346,7 +345,6 @@ int main(int argc, char **argv) {
   int multipathfilter_stages = 0;
   bool ifrate_offset_enable = false;
   double ifrate_offset_ppm = 0;
-  bool enable_fm_afc = false;
   std::string config_str;
   std::string devtype_str;
   DevType devtype;
@@ -402,11 +400,10 @@ int main(int argc, char **argv) {
       {"squelch", required_argument, nullptr, 'l'},
       {"multipathfilter", required_argument, nullptr, 'E'},
       {"ifrateppm", optional_argument, nullptr, 'r'},
-      {"afc", optional_argument, nullptr, 'A'},
       {nullptr, no_argument, nullptr, 0}};
 
   int c, longindex;
-  while ((c = getopt_long(argc, argv, "m:t:c:d:MR:F:W:G:f:l:P:T:b:qXUE:r:A",
+  while ((c = getopt_long(argc, argv, "m:t:c:d:MR:F:W:G:f:l:P:T:b:qXUE:r:",
                           longopts, &longindex)) >= 0) {
     switch (c) {
     case 'm':
@@ -490,9 +487,6 @@ int main(int argc, char **argv) {
         badarg("-r");
       }
       break;
-    case 'A':
-      enable_fm_afc = true;
-      break;
     default:
       usage();
       fprintf(stderr, "ERROR: Invalid command line options\n");
@@ -899,16 +893,6 @@ int main(int argc, char **argv) {
                              : ppm_average_stages,
       0.0f);
 
-  // Initialize moving average object for FM AFC.
-  const unsigned int fm_afc_average_stages = 1000;
-  MovingAverage<float> fm_afc_average(
-      enable_predownsampling ? fm_afc_average_stages * predownsample_ratio
-                             : fm_afc_average_stages,
-      0.0f);
-  const unsigned int fm_afc_hz_step = 10;
-  FineTuner fm_afc_finetuner((unsigned int)fm_target_rate / fm_afc_hz_step);
-  float fm_afc_offset_sum = 0.0;
-
   unsigned int nchannel = stereo ? 2 : 1;
 
   // If buffering enabled, start background output thread.
@@ -960,7 +944,6 @@ int main(int argc, char **argv) {
     // Pull next block from source buffer.
     IQSampleVector iqsamples = source_buffer.pull();
 
-    IQSampleVector if_afc_samples;
     IQSampleVector if_shifted_samples;
     IQSampleVector if_downsampled_samples;
     IQSampleVector if_samples;
@@ -976,27 +959,13 @@ int main(int argc, char **argv) {
     // so long as the stability of the receiver device is
     // within the range of +- 1ppm (~100Hz or less).
 
-    // Experimental FM broadcast AFC code
-    if (modtype == ModType::FM && enable_fm_afc) {
-      // get the frequency offset
-      fm_afc_average.feed(fm.get_tuning_offset());
-      if ((block % fm_afc_average_stages) == 0) {
-        fm_afc_offset_sum += 0.7 * fm_afc_average.average();
-        fm_afc_finetuner.set_freq_shift(
-            -((unsigned int)std::round(fm_afc_offset_sum / fm_afc_hz_step)));
-      }
-      fm_afc_finetuner.process(iqsamples, if_afc_samples);
-    } else {
-      if_afc_samples = std::move(iqsamples);
-    }
-
     if (enable_fs_fourth_downconverter) {
       // Fs/4 downconvering is required
       // to avoid frequency zero offset
       // because Airspy HF+ and RTL-SDR are Zero IF receivers
-      fourth_downconverter.process(if_afc_samples, if_shifted_samples);
+      fourth_downconverter.process(iqsamples, if_shifted_samples);
     } else {
-      if_shifted_samples = std::move(if_afc_samples);
+      if_shifted_samples = std::move(iqsamples);
     }
 
     // Downsample if pre-downsampling is enable_downsampling