[pjsip] Echo problem

Kapil Pendse kapil.pendse at gmail.com
Thu Aug 12 01:26:13 CDT 2010

Hello everyone,

I'm using pjsip-1.5.5. Compiled one copy for Windows Mobile running on Sony
Xperia X1 phones. Compiled another copy for Windows XP laptop.

I've modified the 'pjsua' apps slightly such that there are 4 phones that
call in to this one laptop. The laptop, joins them all in a conference. All
of this over WiFi.

Audio goes through well and all phones are able to communicate with each
other. But there is this echo on each phone. Whatever is spoken in phone-1
is echoed back to phone-1 after about 1~2 seconds (after it is heard on the
other phones).

The laptop's mic and speakers are muted, and port 0 of laptop is NOT
connected to the rest of the conference.

All phones are equipped with headset, so that the backpanel 'speakerphone'
is NOT being used.

Conference bridge connections:

phone-1 - port 3 = transmitting to ports 4,5,6
phone-2 - port 4 = transmitting to ports 3,5,6
phone-3 - port 5 = transmitting to ports 3,4,6
phone-4 - port 6 = transmitting to ports 3,4,5

I tried to use the Echo cancellation algorithm (ec-tail=default 256). Also
tried smaller values of ec-tail. But the moment I use anything other than
ec-tail=0, the phone's just can't handle it. The app bogs down the CPU and
audio becomes horrible. The app's UI stops responding. So I'm guessing the
algorithm is too heavy for the cellphone CPU. I saw in a post that there was
a lighter "echo suppression" algorithm available, but didn't figure out
where in the code it was. Is that the default anyway?

What could be done to get around this echo problem? Any help and suggestions
would be appreciated.

Thanks and best regards,

"The Power to Imagine, is The Power to Create!"
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