[Freeswitch-users] echo cancellation on PRI cards

[Anthony Knight]

Thanks for the feedback.
I have plenty of experience with IVRs and Dialogic cards (starting with
D121/LSI120s and SS96s under DOS in the 90's all the way up to Intel's
DM/Vs) and didn't ever have a problem with DTMF collection with ISDN PRI
lines except occasionally with wireless and cell phones (Bad line quality).

These new cards are so much cheaper than the Dialogic cards were, I should
just buy the version with the cancellers.

Tony


On Tue, Mar 17, 2009 at 11:36 AM, Steve Underwood <steveu at coppice.org>wrote:

> David Knell wrote:
> > Steve Underwood wrote:
> >>> When there is Echo being generated from the far end, usually in a
> >>> bridged call. If you application is just an IVR, with no far end
> >>> connectivity, then you shouldn't need an echo can. If you are bridging
> >>> calls, then at some point you may need it, depending on what else is
> >>> in the loop.
> >>>
> >> This is VERY VERY WRONG. IVRs badly need echo cancellation. Without it
> >> they give very poor reliability detecting DTMF while the prompts are
> >> playing. If the system uses voice recognition, its reliability will be
> >> even worse.
> >>
> > With respect, this is at best half true.  DTMF detection has always
> > worked just fine
> > without echo cancellation - the Dialogic, Aculab and Rhetorex cards
> > which I used
> > in the late 1990s managed it perfectly well; if the DTMF detection
> > code in * and FS
> > can't, then maybe that's something for its author to look at ;-)
> Try reading the Dialogic and Aculab documentation. Those cards used
> quite a bit of their DSP capability to remove the spillback of outgoing
> voice into their DTMF receivers. You'll find the DTMF detector in
> spandsp (not necessarily the ones in * or FS, which have been altered a
> bit) is superior to either Dialogic or Aculab's.
> > ASR - yes, maybe, but L&H's ASR1500 used to work perfectly well on the
> > same
> > hardware above back in the day.  I'd be interested to see results of
> > testing an ASR
> > engine in with echo; unfortunately, most vendors appear to prohibit
> > the publication
> > of test results in their licensing.
> L&H used to work fine with the J series Dialogic cards. The Dialogic
> documents go into considerable details about the echo cancellation
> arrangements to make that happen.
>
> Regards,
> Steve
>
>
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