[asterisk-users] Can I increase DTMF sensitivity?

[Steve Underwood]

Steve Edwards wrote:

> I have a client that is complaining that they are having trouble with 
> Asterisk not reliably recognizing DTMF from some phones. The calls are 
> being delivered by ATT & Qwest over PRI to te410p's with firmware that 
> was upgraded about 10 months ago.
>
> Can I tweak the "amplitude" and duration of what Asterisk considers a 
> keypress? (I'm in the US if it matters.)
>
> What will happen if I tweak too much?
>
> Can I measure the amplitude and duration of a keypress to help 
> identify the phones?

Tweaking is almost never the answer. The DTMF detector will detect a 
wide range of mangled DTMF tones correctly. If it can't detect what you 
are receiving on a clean digital line, something serious is wrong. The 
likely candidates are:

- You have frame slips, because your T1 is not clocked properly, or 
because your PCI bus is not keeping up. The DTMF detector was modified 
to be somewhat tolerant of hiccups in the data, but it can still be 
fooled, especially if a big chunk of audio goes missing.

- You have the gain turned up so far, the signal is clipping. It sounds 
like that shouldn't be an issue, since if the DTMF clips the voice must 
sound awful. Well, I get regular wave files sent to me where the gain 
*is* set that high, and people say the voice has no problem.

- People are using really really crappy phones. There are quite a few 
phones that just never dial reliably. Its hard to see why people put up 
with them, but they do.

Steve