[pjsip] Problem with Echo Canceller on PDAs (windows mobile 5.0 / Pocket PCs)

Ramzi Touma rtt00 at aub.edu.lb
Tue May 20 11:52:58 EDT 2008


I am having problems with the echo canceller on windows CE (PDAs / Pocket
PCs). I tried it on several different models of these devices. I am using
the wince_demos project, pcmu with a ptime of 40 and noVAD. I also included
the the config_site_sample that disables the WSOLA (in case there is a
processing issue on such small devices). I am getting unacceptable sound
performance whenever I enable the echo canceller by setting the ec_tail to
any value other than 0. If I were to describe what sort of sound problem I
am encountering then it is as follows: when echo canceller is disabled, I
get  a good sense of converstation, i.e. both ends here each other well with
a relatively good sound quality having very few or no drop outs at all. But
ofcourse the echo is heard whenever headphones are not used on the PDAs. Now
when I enable the echo canceller, I notice a lot of drop outs in the
conversation specially when a person is initially talking and the other
tries to talk as well (probably here the echo canceller is blocking the
microphone which has real voice and considers it as noise or something). To
get the other person's voice to be heard, both parties should go quiet for 1
or 2 seconds and then the first to start talking will be heard while the
other will be blocked out (not entirely but enough to make the conversation
unclear) .


To make things clearer, if A and B are in a conversation, when A  starts to
speak, B hears A but if B attempts to speak A while A is still talking, A
will not hear B talking for some while; causing a lot of drop out and
yielding the conversation useless.


I hope I made myself clear somehow J 





Ramzi T. Touma

Electrical and Computer Engineering

American University of Beirut

P.O. Box 11-0236/ 5555

Riad el Solh Square 1107 - 2020

Email:  <http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org>
rtt00 at aub.edu.lb


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