[Asterisk-Users] BAD/GOOD Echo Cancel

Matt mattl at xgforce.com
Mon Feb 6 12:34:14 MST 2006


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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