Re: Min DTMF Gap

On Fri, Jan 17, 2014 at 4:39 PM, Gunnar Hellstrom <
gunnar.hellstrom@omnitor.se> wrote:

> On 2014-01-17 18:35, Cullen Jennings (fluffy) wrote:
>
>>
>> We leave the default tone duration at 100 ms.
>>
> Why this long tone? All columns show minimum 40 ms for duration.
>
> If you want to guarantee the minimum total length of tone + gap to be 125
> ms as required by Australia, it would make more sense to set the default
> tone to 55 ms.
> Then default tone + default gap is 125 ms, and this is also very close to
> the maximum rate set by Japan and Brazil.
>
> Regarding all problems with misbehaving echo cancellers in VoIP gateways,
> I think it is good to not push these figures to its extremes.
>
> So, my proposals for default figures are 55 ms tone and 70 ms gap.
>
> And minimums as Cullen's proposal.
>
>
I would recommend to keep default tone length at least at 70 ms.
Justification is that it should be long enough to loose a packet of G.711
audio (which normally is no more then 30 ms long) and still be long enough
to be recognized.

This being said, I do not see any reason to reduce default 100 ms tone
duration. The limitation in Q.24 is on the max rate. There no harm at
sending DTMF digits at a lower rates.
_____________
Roman Shpount