Merge pull request #1255 from gqrx-sdr/wav-file-attenuation

Add 6 dB attentuation to WAV file recordings

resources/news.txt

@@ -22,6 +22,7 @@
   IMPROVED: Plot can be zoomed & resized while DSP is stopped.
   IMPROVED: FFT window setting is stored as a string.
   IMPROVED: Waterfall span setting is stored in milliseconds.
+  IMPROVED: Added 6 dB attenuation to WAV file recordings to prevent clipping.
    CHANGED: Default narrow FM deviation increased to 5 kHz.
      FIXED: Time on waterfall is calculated correctly.
      FIXED: Frequency is correctly rounded in I/Q filenames.

src/applications/gqrx/receiver.cpp

@@ -47,6 +47,7 @@
 #endif
 
 #define DEFAULT_AUDIO_GAIN -6.0
+#define WAV_FILE_GAIN 0.5
 #define TARGET_QUAD_RATE 1e6
 
 /**
@@ -1020,6 +1021,9 @@ receiver::status receiver::start_audio_recording(const std::string filename)
         return STATUS_ERROR;
     }
 
+    wav_gain0 = gr::blocks::multiply_const_ff::make(WAV_FILE_GAIN);
+    wav_gain1 = gr::blocks::multiply_const_ff::make(WAV_FILE_GAIN);
+
     // if this fails, we don't want to go and crash now, do we
     try {
 #if GNURADIO_VERSION < 0x030900
@@ -1038,8 +1042,10 @@ receiver::status receiver::start_audio_recording(const std::string filename)
     }
 
     tb->lock();
-    tb->connect(rx, 0, wav_sink, 0);
-    tb->connect(rx, 1, wav_sink, 1);
+    tb->connect(rx, 0, wav_gain0, 0);
+    tb->connect(rx, 1, wav_gain1, 0);
+    tb->connect(wav_gain0, 0, wav_sink, 0);
+    tb->connect(wav_gain1, 0, wav_sink, 1);
     tb->unlock();
     d_recording_wav = true;
 
@@ -1068,15 +1074,19 @@ receiver::status receiver::stop_audio_recording()
     // not strictly necessary to lock but I think it is safer
     tb->lock();
     wav_sink->close();
-    tb->disconnect(rx, 0, wav_sink, 0);
-    tb->disconnect(rx, 1, wav_sink, 1);
+    tb->disconnect(rx, 0, wav_gain0, 0);
+    tb->disconnect(rx, 1, wav_gain1, 0);
+    tb->disconnect(wav_gain0, 0, wav_sink, 0);
+    tb->disconnect(wav_gain1, 0, wav_sink, 1);
 
     // Temporary workaround for https://github.com/gnuradio/gnuradio/issues/5436
     tb->disconnect(ddc, 0, rx, 0);
     tb->connect(ddc, 0, rx, 0);
     // End temporary workaronud
 
     tb->unlock();
+    wav_gain0.reset();
+    wav_gain1.reset();
     wav_sink.reset();
     d_recording_wav = false;
 
@@ -1395,8 +1405,10 @@ void receiver::connect_all(rx_chain type)
     // Recorders and sniffers
     if (d_recording_wav)
     {
-        tb->connect(rx, 0, wav_sink, 0);
-        tb->connect(rx, 1, wav_sink, 1);
+        tb->connect(rx, 0, wav_gain0, 0);
+        tb->connect(rx, 1, wav_gain1, 0);
+        tb->connect(wav_gain0, 0, wav_sink, 0);
+        tb->connect(wav_gain1, 0, wav_sink, 1);
     }
 
     if (d_sniffer_active)

src/applications/gqrx/receiver.h

@@ -271,6 +271,8 @@ class receiver
 
     gr::blocks::multiply_const_ff::sptr audio_gain0; /*!< Audio gain block. */
     gr::blocks::multiply_const_ff::sptr audio_gain1; /*!< Audio gain block. */
+    gr::blocks::multiply_const_ff::sptr wav_gain0; /*!< WAV file gain block. */
+    gr::blocks::multiply_const_ff::sptr wav_gain1; /*!< WAV file gain block. */
 
     gr::blocks::file_sink::sptr         iq_sink;     /*!< I/Q file sink. */