Re: DTMF v4

Regarding Gunnar's comment about Australian DTMF being 'different' and
needing checking - the current National CE Standard (S003-1_2010r.pdf)
still states DTMF tones must be 40ms minimum duration with *70 ms minimum
break between tones*.

Barry Dingle


On Sat, Dec 15, 2012 at 9:30 AM, Gunnar Hellström <
gunnar.hellstrom@omnitor.se> wrote:

>  On 2012-12-14 22:10, Roman Shpount wrote:
>
> WebRTC-SIP Interworking Requirements Draft states that:
>
> A3-4 WebRTC MUST provide a means for the Javascript application to invoke
> [RFC4733] DTMF events to be generated, and their duration, with a default
> duration of 100ms.
>
> A3-6 WebRTC MUST NOT generate [RFC4733] events closer than 50ms
> back-to-back.  In other words, even if                      the Javascript
> calls the API repeatedly or provides a string of digits to send, the
> browser must enforce a minimum of 50ms inter-event gap.
>
> There are several fairly old recommendations, such as ITU-T V.18, on which
> these values are based, but the bottom line that these values are usually
> considered safe.
>
>   ITU-T Recommendation Q.24 is the origin of the timing of DTMF.
> http://www.itu.int/rec/T-REC-Q.24-198811-I/en
> A table is given in Annex A for some countries.
>
>
> It seems that a minimum 40 ms signal and minimum 30-70 ms gap are common
> requirements.
> ( the 70 ms gap is Australia. I suggest that you check if they still
> require that value. )
>
> So 50  ms signal and 50 ms gap sound good for real produced values except
> for what is said for Australia in Q.24.
> But some countries seemed to require a sum of signal + gap to be more than
> 120 or 125 ms, while more common seems to be 100 ms.
>
> I assume that the duration mentioned in A3-4 is meant to be signal time
> plus silence time. Right?
>
> /Gunnar
>
>  _____________
>
> Roman Shpount
>
>  On Fri, Dec 14, 2012 at 3:53 PM, Martin Thomson <martin.thomson@gmail.com
> > wrote:
>
>> On 14 December 2012 12:40, Harald Alvestrand <harald@alvestrand.no>
>> wrote:
>> > Bernard mentioned a minimum gap (I think he said 50 ms), but I'm not
>> sure
>> > where that came from.
>>
>>  Minimum values come from experience with IVR interoperation for cases
>> where the tone is subsequently mixed into the audio.  Too short a tone
>> (or gap) and some IVRs fail to detect the tone.  I've seen minimum
>> tone duration of 100ms and gap of 50ms in some cases, though more
>> conservative values might be appropriate.  I have no good data to back
>> any specific choice.  I expect fluffy has more data than I.
>>
>>
>
>