osmoradio: Fix disabling of emphasis

src/radio/main.c

@@ -136,7 +136,7 @@ void print_help(const char *arg0)
 	printf("        Give modulation index of amplitude modulated signal. (default %.0f)\n", modulation_index);
 	printf(" -E --emphasis <uS> | 0\n");
 	printf("        Use given time constant of pre- and de-emphasis for frequency\n");
-	printf("        modulation. Give 0 to disbale. (default = %.0f uS)\n", time_constant_us);
+	printf("        modulation. Give 0 to disbale emphasis. (default = %.0f uS)\n", time_constant_us);
 	printf("        VHF broadcast 50 uS in Europe and 75 uS in the United States.\n");
 	printf("        Other radio FM should use 530 uS, to cover complete speech spectrum.\n");
 	printf(" -V --volume %.3f\n", volume);

src/radio/radio.c

@@ -235,14 +235,17 @@ int radio_init(radio_t *radio, int latspl, int samplerate, const char *tx_wave_f
 	/* init filters (using signal sample rate) */
 	switch (radio->modulation) {
 	case MODULATION_FM:
-		/* time constant */
-		PDEBUG(DRADIO, DEBUG_INFO, "Using emphasis cut-off at %.0f Hz.\n", timeconstant2cutoff(time_constant_us));
-		rc = init_emphasis(&radio->fm_emphasis[0], radio->signal_samplerate, timeconstant2cutoff(time_constant_us), DC_CUTOFF, radio->audio_bandwidth);
-		if (rc < 0)
-			goto error;
-		rc = init_emphasis(&radio->fm_emphasis[1], radio->signal_samplerate, timeconstant2cutoff(time_constant_us), DC_CUTOFF, radio->audio_bandwidth);
-		if (rc < 0)
-			goto error;
+		if (time_constant_us > 0.0) {
+			radio->emphasis = 1;
+			/* time constant */
+			PDEBUG(DRADIO, DEBUG_INFO, "Using emphasis cut-off at %.0f Hz.\n", timeconstant2cutoff(time_constant_us));
+			rc = init_emphasis(&radio->fm_emphasis[0], radio->signal_samplerate, timeconstant2cutoff(time_constant_us), DC_CUTOFF, radio->audio_bandwidth);
+			if (rc < 0)
+				goto error;
+			rc = init_emphasis(&radio->fm_emphasis[1], radio->signal_samplerate, timeconstant2cutoff(time_constant_us), DC_CUTOFF, radio->audio_bandwidth);
+			if (rc < 0)
+				goto error;
+		}
 		rc = fm_mod_init(&radio->fm_mod, radio->signal_samplerate, 0.0, 1.0);
 		if (rc < 0)
 			goto error;
@@ -552,10 +555,12 @@ int radio_tx(radio_t *radio, float *baseband, int signal_num)
 	 * and modulate */
 	switch (radio->modulation) {
 	case MODULATION_FM:
-		pre_emphasis(&radio->fm_emphasis[0], signal_samples[0], signal_num);
+		if (radio->emphasis)
+			pre_emphasis(&radio->fm_emphasis[0], signal_samples[0], signal_num);
 		clipper_process(signal_samples[0], signal_num);
 		if (radio->stereo) {
-			pre_emphasis(&radio->fm_emphasis[1], signal_samples[1], signal_num);
+			if (radio->emphasis)
+				pre_emphasis(&radio->fm_emphasis[1], signal_samples[1], signal_num);
 			clipper_process(signal_samples[1], signal_num);
 			/* add pilot tone */
 			double phasestep = radio->pilot_phasestep;
@@ -643,11 +648,13 @@ int radio_rx(radio_t *radio, float *baseband, int signal_num)
 			iir_process(&radio->rx_lp_sum, samples[0], signal_num);
 			iir_process(&radio->rx_lp_diff, samples[1], signal_num);
 		}
-		dc_filter(&radio->fm_emphasis[0], samples[0], signal_num);
-		de_emphasis(&radio->fm_emphasis[0], samples[0], signal_num);
-		if (radio->stereo) {
-			dc_filter(&radio->fm_emphasis[1], samples[1], signal_num);
-			de_emphasis(&radio->fm_emphasis[1], samples[1], signal_num);
+		if (radio->emphasis) {
+			dc_filter(&radio->fm_emphasis[0], samples[0], signal_num);
+			de_emphasis(&radio->fm_emphasis[0], samples[0], signal_num);
+			if (radio->stereo) {
+				dc_filter(&radio->fm_emphasis[1], samples[1], signal_num);
+				de_emphasis(&radio->fm_emphasis[1], samples[1], signal_num);
+			}
 		}
 		break;
 	case MODULATION_AM_DSB:

src/radio/radio.h

@@ -30,6 +30,7 @@ typedef struct radio {
 	double		volume;			/* volume change (gain/dampen) */
 	int		stereo;			/* use stere FM */
 	int		rds, rds2;		/* use RDS */
+	int		emphasis;		/* use pre-/de-emphasis with FM */
 	/* audio stage */
 	double		tx_audio_samplerate;	/* sample rate of audio source */
 	double		rx_audio_samplerate;	/* sample rate of audio sink */