diff --git a/src/common/Makefile.am b/src/common/Makefile.am
index ce65997..e63ac2c 100644
--- a/src/common/Makefile.am
+++ b/src/common/Makefile.am
@@ -10,6 +10,7 @@ libcommon_a_SOURCES = \
 	../common/jitter.c \
 	../common/loss.c \
 	../common/filter.c \
+	../common/dtmf.c \
 	../common/samplerate.c \
 	../common/call.c \
 	../common/freiton.c \
diff --git a/src/common/dtmf.c b/src/common/dtmf.c
new file mode 100644
index 0000000..b052fd5
--- /dev/null
+++ b/src/common/dtmf.c
@@ -0,0 +1,118 @@
+/* DTMF coder
+ *
+ * (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 "dtmf.h"
+
+#define PI		M_PI
+
+#define TX_PEAK_DTMF	7000   /* single dtmf tone peak (note this is half to total peak) */ 
+#define DTMF_DURATION	0.100   /* duration in seconds */
+
+int dsp_sine_dtmf[256];
+
+void dtmf_init(dtmf_t *dtmf, int samplerate)
+{
+	int i;
+
+	memset(dtmf, 0, sizeof(*dtmf));
+	dtmf->samplerate = samplerate;
+	dtmf->max = (int)((double)samplerate * DTMF_DURATION + 0.5);
+
+	// FIXME: do this globally and not per instance */
+	for (i = 0; i < 256; i++)
+		dsp_sine_dtmf[i] = (int)(sin((double)i / 256.0 * 2.0 * PI) * TX_PEAK_DTMF);
+}
+
+/* set dtmf tone */
+void dtmf_set_tone(dtmf_t *dtmf, char tone)
+{
+	double f1, f2;
+
+	switch(tone) {
+		case '1': f1 = 697.0; f2 = 1209.0; break;
+		case '2': f1 = 697.0; f2 = 1336.0; break;
+		case '3': f1 = 697.0; f2 = 1477.0; break;
+	case'a':case 'A': f1 = 697.0; f2 = 1633.0; break;
+		case '4': f1 = 770.0; f2 = 1209.0; break;
+		case '5': f1 = 770.0; f2 = 1336.0; break;
+		case '6': f1 = 770.0; f2 = 1477.0; break;
+	case'b':case 'B': f1 = 770.0; f2 = 1633.0; break;
+		case '7': f1 = 852.0; f2 = 1209.0; break;
+		case '8': f1 = 852.0; f2 = 1336.0; break;
+		case '9': f1 = 852.0; f2 = 1477.0; break;
+	case'c':case 'C': f1 = 852.0; f2 = 1633.0; break;
+		case '*': f1 = 941.0; f2 = 1209.0; break;
+		case '0': f1 = 941.0; f2 = 1336.0; break;
+		case '#': f1 = 941.0; f2 = 1477.0; break;
+	case'd':case 'D': f1 = 941.0; f2 = 1633.0; break;
+	default:
+		dtmf->tone = 0;
+		return;
+	}
+	dtmf->tone = tone;
+	dtmf->pos = 0;
+	dtmf->phaseshift256[0] = 256.0 / ((double)dtmf->samplerate / f1);
+	dtmf->phaseshift256[1] = 256.0 / ((double)dtmf->samplerate / f2);
+}
+
+/* Generate audio stream from DTMF tone. Keep phase for next call of function. */
+void dtmf_tone(dtmf_t *dtmf, int16_t *samples, int length)
+{
+        double *phaseshift, *phase;
+	int i, pos, max;
+
+	/* use silence, if no tone */
+	if (!dtmf->tone) {
+		memset(samples, 0, length * sizeof(*samples));
+		return;
+	}
+
+	phaseshift = dtmf->phaseshift256;
+	phase = dtmf->phase256;
+	pos = dtmf->pos;
+	max = dtmf->max;
+
+	for (i = 0; i < length; i++) {
+		*samples++ = dsp_sine_dtmf[((uint8_t)phase[0]) & 0xff]
+			   + dsp_sine_dtmf[((uint8_t)phase[1]) & 0xff];
+		phase[0] += phaseshift[0];
+		if (phase[0] >= 256)
+			phase[0] -= 256;
+		phase[1] += phaseshift[1];
+		if (phase[1] >= 256)
+			phase[1] -= 256;
+
+		/* tone ends */
+		if (++pos == max) {
+			dtmf->tone = 0;
+			break;
+		}
+	}
+	length -= i;
+
+	dtmf->pos = pos;
+
+	/* if tone ends, fill rest with silence */
+	if (length)
+		memset(samples, 0, length * sizeof(*samples));
+}
+
diff --git a/src/common/dtmf.h b/src/common/dtmf.h
new file mode 100644
index 0000000..a0120db
--- /dev/null
+++ b/src/common/dtmf.h
@@ -0,0 +1,14 @@
+
+typedef struct dtmf {
+	int	samplerate;		/* samplerate */
+	char	tone;			/* current tone to be played */
+	int	pos;			/* sample counter for tone */
+	int	max;			/* max number of samples for tone duration */
+	double	phaseshift256[2];	/* how much the phase of sine wave changes per sample */
+	double	phase256[2];		/* current phase */
+} dtmf_t;
+
+void dtmf_init(dtmf_t *dtmf, int samplerate);
+void dtmf_set_tone(dtmf_t *dtmf, char tone);
+void dtmf_tone(dtmf_t *dtmf, int16_t *samples, int length);
+