----- Original Message -----
From: "Steve Underwood" <[EMAIL PROTECTED]>
To: "Asterisk Users Mailing List - Non-Commercial Discussion"
<[email protected]>
Sent: Friday, August 05, 2005 7:39 PM
Subject: Re: [Asterisk-Users] Is this echo problem down to IP Phone
hardware?
Kris Boutilier wrote:
This known as is 'acoustic echo' or 'room reverb' and involves mathematics
that is quite a bit different from that used when cancelling regular
'reflected electrical signal' echos, as the signal is being acousically
distorted as it echos around the room. On many handsfree handsets it
doesn't manifest itself until you move into a physically large room, which
increases the reflection delay and overwhelms the internal mechanisms.
The maths is exactly the same. However, it is certainly true that a lot of
acoustic echo cancellers don't deal with long enough echoes to be
effective in large spaces.
It would need to be handled internally by the handset or you would need
to insert a hardware echo canceller capable of dealing with this type of
echo, assuming your signal is exposed on a T1 somewhere. If it's IP all
the way for you then you're really just down to the handset vendors as
far as I know - Asterisk doesn't currently offer any form of echo
cancellation on the VoIP side.
In the IP world the echo must be killed by the phone itself. You cannot
echo cancel on the IP side of a switch like Asterisk. The echo path length
needs to be constant for any known echo cancellation process to work. IP
path lengths are not constant.
Hello
I have a Grandstream GXP2000 with latest firmware. When I use it holding
the handpiece I don't hear any echo - neither does other end. However,
if I use it handsfree, the other end notices echo when they speak - ie
their voice is echoy. I hear their voice being a bit echoy.
The Grandstreams are much maligned, but they actually do a better job in
this area than most products. As said above, if you are using this in a
large space the echo canceller in the phone may not cancel a long enough
echo to be very effective. If it fails to kill the echo in a small room
something is wrong.
* The room is 15 foot by 22 foot. Not massive. When you say something is
wrong, what should I be looking at? I will buy a Cisco 7940 as suggested
previously to see if the handset does make a difference.
In my sip.conf I allow ulaw, alaw, g723.1, g729 and gsm. Should I tighten
this down to fewer? Which ones? More?
Is this purely down to the IP Phone? Is there anything I can do about
it? I considered buying a more expensive phone - eg a Snom to see what
they were like for echo. Is there something I can do with the Asterisk?
codec to use? Anything?
A snom might be a poor choice. People tell me they don't even echo cancel
the handset. If a hard of hearing user turns up the handset volume the
caller hears considerable echo.
* Thanks. I will test with a Cisco.
Regards,
Steve
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