minimodem: --Xrxnoise=factor adds test noise

Injects random noise to input signal (in memory) before analysis.

src/minimodem.c

@@ -389,6 +389,8 @@ main( int argc, char*argv[] )
     float tx_amplitude = 1.0;
     unsigned int tx_sin_table_len = 4096;
 
+    float rxnoise_factor = 0.0;
+
     /* validate the default system audio mechanism */
 #if !(USE_PULSEAUDIO || USE_ALSA)
 # define _MINIMODEM_NO_SYSTEM_AUDIO
@@ -411,6 +413,7 @@ main( int argc, char*argv[] )
 	MINIMODEM_OPT_LUT,
 	MINIMODEM_OPT_FLOAT_SAMPLES,
 	MINIMODEM_OPT_BENCHMARKS,
+	MINIMODEM_OPT_XRXNOISE,
     };
 
     while ( 1 ) {
@@ -439,6 +442,7 @@ main( int argc, char*argv[] )
 	    { "lut",		1, 0, MINIMODEM_OPT_LUT },
 	    { "float-samples",	0, 0, MINIMODEM_OPT_FLOAT_SAMPLES },
 	    { "benchmarks",	0, 0, MINIMODEM_OPT_BENCHMARKS },
+	    { "Xrxnoise",	1, 0, MINIMODEM_OPT_XRXNOISE },
 	    { 0 }
 	};
 	c = getopt_long(argc, argv, "Vtrc:l:a85f:b:v:M:S:T:qAR:",
@@ -525,6 +529,9 @@ main( int argc, char*argv[] )
 			benchmarks();
 			exit(0);
 			break;
+	    case MINIMODEM_OPT_XRXNOISE:
+			rxnoise_factor = atof(optarg);
+			break;
 	    default:
 			usage();
 	}
@@ -698,6 +705,8 @@ main( int argc, char*argv[] )
     if ( ! sa )
         return 1;
 
+    if ( rxnoise_factor != 0.0 )
+	simpleaudio_set_rxnoise(sa, rxnoise_factor);
 
     /*
      * Prepare the input sample chunk rate

src/simpleaudio-sndfile.c

@@ -24,6 +24,7 @@
 #if USE_SNDFILE
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <malloc.h>
 #include <string.h>
 #include <assert.h>
@@ -60,6 +61,15 @@ sa_sndfile_read( simpleaudio *sa, void *buf, size_t nframes )
 	sf_perror(s);
 	return -1;
     }
+
+    if ( sa->rxnoise != 0.0 ) {
+	int i;
+	float *fbuf = buf;
+	float f = sa->rxnoise * 2;
+	for ( i=0; i<nframes; i++ )
+	    fbuf[i] += (drand48() - 0.5) * f;
+    }
+
     // fprintf(stderr, "sf_read: nframes=%ld n=%d\n", nframes, n);
     return n;
 }

src/simpleaudio.c

@@ -149,6 +149,12 @@ simpleaudio_get_samplesize( simpleaudio *sa )
     return sa->samplesize;
 }
 
+void
+simpleaudio_set_rxnoise( simpleaudio *sa, float rxnoise_factor )
+{
+    sa->rxnoise = rxnoise_factor;
+}
+
 ssize_t
 simpleaudio_read( simpleaudio *sa, void *buf, size_t nframes )
 {

src/simpleaudio.h

@@ -75,6 +75,9 @@ simpleaudio_get_format( simpleaudio *sa );
 unsigned int
 simpleaudio_get_samplesize( simpleaudio *sa );
 
+void
+simpleaudio_set_rxnoise( simpleaudio *sa, float rxnoise_factor );
+
 ssize_t
 simpleaudio_read( simpleaudio *sa, void *buf, size_t nframes );
 

src/simpleaudio_internal.h

@@ -35,6 +35,7 @@ struct simpleaudio {
 	void *		backend_handle;
 	unsigned int	samplesize;
 	unsigned int	backend_framesize;
+	float		rxnoise;		// only for the sndfile backend
 };
 
 struct simpleaudio_backend {