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

[Eric "ManxPower" Wieling]

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!