[Asterisk-Users] BAD/GOOD Echo Cancel

[Matt]

This is very true, you must use hardware echo cancel and voice processing.
we use sangoma 104d hardware echo cancel card, it eliminates all echoes we
had.

Best Regards

Matt
----- Original Message ----- 
From: "Steve Underwood" <steveu at coppice.org>
To: "Asterisk Users Mailing List - Non-Commercial Discussion"
<asterisk-users at lists.digium.com>
Sent: Monday, February 06, 2006 6:09 AM
Subject: Re: [Asterisk-Users] BAD/GOOD Echo Cancel


> James Harper wrote:
>
> >>virtually all software echo cancelers cannot get double echo removed
> >>completly.  It can get the first one but not the second one.  There
> >>
> >>
> >are
> >
> >
> >>instances where you get a 2nd echo, so ...  Asterisk is no exception
> >>from this afaik nothing software only based is.
> >>
> >>If you really want good echo cancelation a hardware solution is the
> >>
> >>
> >way
> >
> >
> >>to go.
> >>
> >>
> >>
> >
> >Just an enquiring mind wanting to know, but how is a hardware solution
> >different to a software solution? The echo cancellers in the Digium
> >hardware presumably just use the same sort of algorithms as the software
> >versions, so it is just that they are dedicated and perform better, that
> >they are closer to the source of the echo, or some other thing that I've
> >overlooked?
> >
> >
> There isn't much difference, except for the amount of CPU taken, and the
> issue that software echo cancellation forces the device to use very
> short buffers. He's talking rubbish. Hardware echo cancellation
> certainly eases the timing constraints on the E1/T1 card to host
> processor interface. A lot more buffering can occur if the host does not
> do echo cancelling. A 20ms buffer on a PCI card will practically all the
> quirky timing issues people see go away. However 20ms of buffering would
> badly hurt an echo canceller's convergence.
>
> Most hardware cancellers, are actually software cancellers. The software
> just runs in a DSP (often a customised one) instead of the host
> processor. Some are a hybrid hardware/software design. Few are pure
> hardware.
>
> There are no standard algorithms for echo cancellation, and no standard
> level of performance. Few cancellers which claim G.168 compliance
> actually pass all the tests. If you look in the small print they
> generally say which tests they do pass. Echo cancellers vary a lot in
> performance, and making them truly robust and efficient is still a
> research topic.
>
> Regards,
> Steve
> \
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