[Freeswitch-users] echo cancellation on PRI cards

[Steve Underwood]

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