Add compander to common part

src/common/Makefile.am

@@ -17,6 +17,7 @@ libcommon_a_SOURCES = \
 	../common/besetztton.c \
 	../common/mncc_sock.c \
 	../common/cause.c \
+	../common/compander.c \
 	../common/sender.c \
 	../common/main_common.c
 

src/common/compander.c

@@ -0,0 +1,132 @@
+/* Compander to use various networks like C-Netz / NMT / AMPS
+ *
+ * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include <math.h>
+#include "compander.h"
+
+/* this is the 0 DB level that stays 0 DB after compression / espansion */
+#define ZERO_DB_LEVEL	16384.0
+
+/* what factor shall the gain raise and fall after given attack/recovery time */
+#define ATTACK_FACTOR	1.5
+#define RECOVERY_FACTOR	0.75
+
+/* Minimum level value to keep state */
+#define ENVELOP_MIN	0.001
+
+static double sqrt_tab[10000];
+
+/*
+ * Generate companding tables according to NMT specification
+ *
+ * Hopefully this is correct
+ *
+ */
+void init_compander(compander_t *state, int samplerate, double attack_ms, double recovery_ms)
+{
+	int i;
+
+	memset(state, 0, sizeof(*state));
+
+	state->envelop_e = 1.0;
+	state->envelop_c = 1.0;
+	/* ITU-T G.162: 1.5 times the steady state after attack_ms */
+	state->step_up = pow(ATTACK_FACTOR, 1000.0 / attack_ms / (double)samplerate);
+
+	/* ITU-T G.162: 0.75 times the steady state after recovery_ms */
+	state->step_down = pow(RECOVERY_FACTOR, 1000.0 / recovery_ms / (double)samplerate);
+
+	// FIXME: make global, not at instance
+	for (i = 0; i < 10000; i++)
+		sqrt_tab[i] = sqrt(i * 0.001);
+}
+
+void compress_audio(compander_t *state, int16_t *samples, int num)
+{
+	int32_t sample;
+	double value, envelop, step_up, step_down;
+	int i;
+
+	step_up = state->step_up;
+	step_down = state->step_down;
+	envelop = state->envelop_c;
+
+//	printf("envelop=%.4f\n", envelop);
+	for (i = 0; i < num; i++) {
+		/* normalize sample value to 0 DB level */
+		value = (double)(*samples) / ZERO_DB_LEVEL;
+
+		if (fabs(value) > envelop)
+			envelop *= step_up;
+		else
+			envelop *= step_down;
+		if (envelop < ENVELOP_MIN)
+			envelop = ENVELOP_MIN;
+
+		value = value / sqrt_tab[(int)(envelop / 0.001)];
+
+		/* convert back from 0 DB level to sample value */
+		sample = (int)(value * ZERO_DB_LEVEL);
+		if (sample > 32767)
+			sample = 32767;
+		else if (sample < -32768)
+			sample = -32768;
+		*samples++ = sample;
+	}
+
+	state->envelop_c = envelop;
+}
+
+void expand_audio(compander_t *state, int16_t *samples, int num)
+{
+	int32_t sample;
+	double value, envelop, step_up, step_down;
+	int i;
+
+	step_up = state->step_up;
+	step_down = state->step_down;
+	envelop = state->envelop_e;
+
+	for (i = 0; i < num; i++) {
+		/* normalize sample value to 0 DB level */
+		value = (double)(*samples) / ZERO_DB_LEVEL;
+
+		if (fabs(value) > envelop)
+			envelop *= step_up;
+		else
+			envelop *= step_down;
+		if (envelop < ENVELOP_MIN)
+			envelop = ENVELOP_MIN;
+
+		value = value * envelop;
+
+		/* convert back from 0 DB level to sample value */
+		sample = (int)(value * ZERO_DB_LEVEL);
+		if (sample > 32767)
+			sample = 32767;
+		else if (sample < -32768)
+			sample = -32768;
+		*samples++ = sample;
+	}
+
+	state->envelop_e = envelop;
+}
+

src/common/compander.h

@@ -0,0 +1,11 @@
+typedef struct compander {
+	double	step_up;
+	double	step_down;
+	double	envelop_c;
+	double	envelop_e;
+} compander_t;
+
+void init_compander(compander_t *state, int samplerate, double attack_ms, double recovery_ms);
+void compress_audio(compander_t *state, int16_t *samples, int num);
+void expand_audio(compander_t *state, int16_t *samples, int num);
+