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AMPS: Add DTX support

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When DTX is enabled (-S dtx=2 or 3), a missing SAT tone causes the receiver
to mute audio and insert a low level of comfort noise.
Also the missing SAT tone will not cause the connection to be terminated.
This commit is contained in:
Andreas Eversberg
2017-05-25 09:57:22 +02:00
parent 2c1ab89723
commit bb64c6b3ba
7 changed files with 65 additions and 26 deletions
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47
src/amps/dsp.c
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@@ -107,17 +107,17 @@
#define SAT_DEVIATION (2000.0 / DBM0_DEVIATION) /* no emphasis */
#define MAX_DISPLAY (8000.0 / DBM0_DEVIATION) /* no emphasis */
#define BITRATE 10000
#define SIG_TONE_CROSSINGS 2000 /* 2000 crossings are 100ms @ 10 KHz */
#define SIG_TONE_MINBITS 950 /* minimum bit durations to detect signaling tone (1000 is perfect for 100 ms) */
#define SIG_TONE_MAXBITS 1050 /* as above, maximum bits */
#define SAT_DURATION 0.100 /* duration of SAT signal measurement */
#define SAT_QUALITY 0.85 /* quality needed to detect sat */
#define SAT_DETECT_COUNT 3 /* number of measures to detect SAT signal (specs say 250ms) */
#define SAT_LOST_COUNT 3 /* number of measures to loose SAT signal (specs say 250ms) */
#define SIG_DETECT_COUNT 3 /* number of measures to detect Signaling Tone */
#define SIG_LOST_COUNT 2 /* number of measures to loose Signaling Tone */
#define SAT_DURATION 0.05 /* duration of SAT signal measurement */
#define SAT_QUALITY 0.85 /* quality needed to detect SAT signal */
#define DTX_LEVEL 0.50 /* SAT level needed to mute/unmute */
#define SIG_QUALITY 0.80 /* quality needed to detect Signaling Tone */
#define SAT_DETECT_COUNT 5 /* number of measures to detect SAT signal (specs say 250ms) */
#define SAT_LOST_COUNT 5 /* number of measures to loose SAT signal (specs say 250ms) */
#define SIG_DETECT_COUNT 6 /* number of measures to detect Signaling Tone */
#define SIG_LOST_COUNT 4 /* number of measures to loose Signaling Tone */
#define CUT_OFF_HIGHPASS 300.0 /* cut off frequency for high pass filter to remove dc level from sound card / sample */
#define BEST_QUALITY 0.68 /* Best possible RX quality */
#define COMFORT_NOISE 0.02 /* audio level of comfort noise (relative to ISDN level) */
static sample_t ramp_up[256], ramp_down[256];
@@ -423,6 +423,18 @@ done:
return count;
}
/* send comfort noise */
static void comfort_noise(sample_t *samples, int length)
{
int i;
int16_t r;
for (i = 0; i < length; i++) {
r = random();
samples[i] = (double)r / 32768.0 * COMFORT_NOISE;
}
}
/* Generate audio stream with SAT signal. Keep phase for next call of function. */
static void sat_encode(amps_t *amps, sample_t *samples, int length)
{
@@ -716,7 +728,7 @@ static void sender_receive_frame(amps_t *amps, sample_t *samples, int length)
}
/* decode signaling tone */
/* decode SAT and signaling tone */
/* compare supervisory signal against noise floor on 5800 Hz */
static void sat_decode(amps_t *amps, sample_t *samples, int length)
{
@@ -737,6 +749,10 @@ static void sat_decode(amps_t *amps, sample_t *samples, int length)
if (amps->sender.loopback || debuglevel == DEBUG_DEBUG) {
PDEBUG_CHAN(DDSP, debuglevel, "Signaling Tone level %.2f%% quality %.0f%%\n", result[2] / FSK_DEVIATION / 0.63662 * 100.0, quality[1] * 100.0);
}
if (quality[0] > SAT_QUALITY && result[0] / SAT_DEVIATION / 0.63662 > DTX_LEVEL)
amps->dtx_state = 1;
else
amps->dtx_state = 0;
if (quality[0] > SAT_QUALITY) {
if (amps->sat_detected == 0) {
amps->sat_detect_count++;
@@ -760,7 +776,7 @@ static void sat_decode(amps_t *amps, sample_t *samples, int length)
} else
amps->sat_detect_count = 0;
}
if (quality[1] > 0.8) {
if (quality[1] > SIG_QUALITY) {
if (amps->sig_detected == 0) {
amps->sig_detect_count++;
if (amps->sig_detect_count == SIG_DETECT_COUNT) {
@@ -785,11 +801,6 @@ static void sat_decode(amps_t *amps, sample_t *samples, int length)
}
}
/* decode signaling/audio */
/* Count SIG_TONE_CROSSINGS of zero crossings, then check if the elapsed bit
* time is between SIG_TONE_MINBITS and SIG_TONE_MAXBITS. If it is, the
* frequency is close to the singalling tone, so it is detected
*/
static void sender_receive_audio(amps_t *amps, sample_t *samples, int length)
{
transaction_t *trans = amps->trans_list;
@@ -813,7 +824,7 @@ static void sender_receive_audio(amps_t *amps, sample_t *samples, int length)
/* receive audio, but only if call established and SAT detected */
if ((amps->dsp_mode == DSP_MODE_AUDIO_RX_AUDIO_TX || amps->dsp_mode == DSP_MODE_AUDIO_RX_FRAME_TX)
&& trans && trans->callref && trans->sat_detected) {
&& trans && trans->callref) {
int pos, count;
int i;
@@ -828,6 +839,8 @@ static void sender_receive_audio(amps_t *amps, sample_t *samples, int length)
for (i = 0; i < count; i++) {
spl[pos++] = samples[i];
if (pos == 160) {
if (amps->dtx_state == 0)
comfort_noise(spl, 160);
call_tx_audio(trans->callref, spl, 160);
pos = 0;
}