[Asterisk-Users] Is this echo problem down to IP Phone hardware?

[Angus Comber]

----- Original Message ----- 
From: "Steve Underwood" <steveu at coppice.org>
To: "Asterisk Users Mailing List - Non-Commercial Discussion" 
<asterisk-users at lists.digium.com>
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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