[asterisk-dev] DTMF detection in dsp.c intolerant?

[Zoa]

Aaaaah, thanks, didn't know that one.

Zoa

Eric "ManxPower" Wieling wrote:
> It will miss digits when you have 2 or more of the same digit in a row. 
>   Example: sent 5551212 and asterisk sees 51212 or 551212
>
> Zoa wrote:
>   
>> Relaxdtmf should give more false positives instead of less detections. ?
>>
>> Zoa
>>
>>
>> Eric "ManxPower" Wieling wrote:
>>     
>>> relaxdtmf=yes is the most common cause of this issue.
>>>
>>> Tony Mountifield wrote:
>>>   
>>>       
>>>> I'm posting this to -dev because I believe the answer will relate to the
>>>> code in dsp.c for DTMF detection.
>>>>
>>>> I have a system connected to the PSTN using EuroISDN over E1 with aLaw
>>>> encoding. When it has answered a call, it listens for a DTMF string which
>>>> contains command codes for the specific application.
>>>>
>>>> Asterisk seems to be very intolerant of slight discrepancies in the DTMF
>>>> tones. We are finding that with calls from certain locations, it will
>>>> often miss digits, even though to the ear the audio sounds clear. Calls
>>>> from other locations will be completely reliable.
>>>>
>>>> I have the system capturing pre-DSP aLaw audio, so I can decode by hand
>>>> and see which digits are missing (using Goldwave's spectrum display
>>>> feature).
>>>>
>>>> Here are two examples of separate calls sending the same string:
>>>>
>>>> http://www.softins.co.uk/dtmf-call-31360.wav
>>>> http://www.softins.co.uk/dtmf-call-31361.wav
>>>>
>>>> The string sent in both cases was *82779736*91856360**
>>>>
>>>> In both cases, Asterisk failed to detect the third 7, and returned the
>>>> string *8277936*91856360**
>>>>
>>>> The audio sounds good to me, so I am at a loss as to what Asterisk didn't
>>>> like. Particularly as it failed in the same way on both occasions, which
>>>> suggests it is not something random such as a system load peak.
>>>>
>>>> The string is always originated by a GSM mobile, and my understanding is
>>>> that DTMF is sent as out-of-band signalling over GSM and then re-generated
>>>> by the GSM to PSTN gateway. Is that correct? So the tones ought to be good.
>>>>
>>>> If anyone has the time and interest to check out these files and offer
>>>> any insights, I would be very grateful indeed. DSP is not my field!
>>>>
>>>> I have a number of other recordings where the tones sound ok but Asterisk
>>>> doesn't like them.
>>>>
>>>> Thanks in advance!
>>>>         
>
> _______________________________________________
> --Bandwidth and Colocation Provided by http://www.api-digital.com--
>
> asterisk-dev mailing list
> To UNSUBSCRIBE or update options visit:
>    http://lists.digium.com/mailman/listinfo/asterisk-dev
>