DTMF Decoding | Telit Cinterion IoT Developer Community
May 10, 2016 - 3:57pm, 3439 views
Hi,
I try to decode DTMF signals on a Cinterion PH8-P modem during a voice call:
1.Enable event reporting:
at^sind="dtmf",1,2,0
2. Doing a MO voice call
atd+49******;
3. Sending DTMF signals from the called phone/modem
In the standard audio mode detection rate is poor. When I switch to audio mode 6 via
at^snfs=6
detection rate becomes much better. Are there other audio settings which can have effects on DTMF decoding?
Thanks in advance,
Michael
Hello,
Generally the DTMF tones are transferred as voice so the quality of the connection matters.
With the SNFS command you choose the preset audio configuration. Each mode is optimized for certain usage. The documentation recommends using mode 6 for DTMF detection so it should be the best choice. Of course you can change the preconfigured parameters manually for fine tuning.
Regards,
Bartłomiej
Hi Bartłomiej,
thanks for your comment.
After power up audio mode is 1 (this is also mentioned in the modem's doc):
Welcome to minicom 2.6.2
OPTIONS:
Compiled on Apr 26 2016, 15:37:23.
Port /dev/ttyACM0, 08:08:24
Press CTRL-A Z for help on special keys
Aat
OK
at^snfs?
^SNFS: 1
OK
Are there any additional informations (beside the modem's doc) at Gemalto about DTMF handling/tuning?
BR,
Michael
Hello,
There's no dedicated document for DTMF decoding. There is only a document describing audio interface. You could probably request it from your module supplier. As audio mode 6 is recommended for DTMF detection I suppose it's settings are optimal for that. So if the detection rate is not satisfactory you could experiment with modifying the settings and check by your own if it can change anything in your particular case.
But if some tones are not recognized maybe the signal quality is very low or changing SIND parameters for DTMF could help or sending longer tones.
Regards,
Bartłomiej
Hi,
the quality of the DTMF tones also depends of the audio codec negociated with the netwrok for voice calls.
Check the documentation of the module your are using , in order to disable the audio codecs with low bitrates.
are you sending the DTMF codes with a external DTMF generator, or just using AT commands. In the second case the AT command requests to the network to reproduce the DTMF in the target. That's the network generates the DTMF code
Regards
ALopez
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