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@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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