[asterisk-dev] DTMF detection and generation code

[Anton]

I also thought the same until found that if I press buttons 
on my Treo650 too fast, DTMF tones did not get recognized 
by my Cisco IVR. I think there are different behaviours 
with different phones.

On 24 April 2006 04:52, Steve Underwood wrote:
> Vahan Yerkanian wrote:
> > Steve Underwood wrote:
> >> With most cellular base stations each press of the
> >> buttons on the phone produces a fixed length DTMF
> >> pulse, with a fixed silence following it. If you press
> >> keys in quick succession, they are buffered up, and
> >> played out as tones at the pace the base station sees
> >> fit. Typically they make the tones very long, for some
> >> reason. 0.5 seconds in many cases. I think your
> >> application sounds broken by design. I've been through
> >> this before, trying to build things which require
> >> rhythmic input. It just doesn't work, unless your
> >> application is limited to plain old analogue land line
> >> phones.
> >
> > DTMF buffer is another useful thing - currently digits
> > sent too fast are guaranteed to be skipped. Ironically,
> > I never get a double or skipped digits from cellular
> > networks - these send DTMFs with loooong durations as
> > the developers have accounted for lossy nature of the
> > cellular technology.
>
> The lossy nature of cellular networks has no impact on
> DTMF. The phones do not generate DTMF. The base stations
> do. The phones merely send messages saying "user pressed
> one", "user pressed five", etc. and they don't tell the
> base station how long it was pressed for. The base
> station generates the DTMF tone in a non-lossy
> environment.
>
> Steve
>
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