[jitsi-users] Jitsi problem

I would like to ask you. I use notebook HP ProBook 4710s, 3,9 GiB RAM,
Intel® Core™2 Duo CPU T5870 @ 2.00GHz × 2 , ATI Mobility Radeon HD 4300
Series with Ubuntu 12.04 LTS 32-bit (only). I have installed Jitsi
(stable version).
I have configured two accounts. I use SIP protocol - audio calls without
any problems.
I have also registered at XMPP jit.si so that I could make a video
conference (videobridge). I have lots troubles with sound quality on
jit.si XMPP. Instant messaging is OK.
Please will you be so kind and advice me what could be wrong when I use
Jisti audio and video calls.
Thank you very much.
With best regards
Lubos Stekly