Audio quality with Xlite + ilbc on Asterisk with jb patch

Hi all,
I have an Asterisk on trixbox machine
I install the patch for jitterbuffer in conference.
I use the softphone Xlite version 3 with ilbc codec.
Now I use jitterbuffer in conference, it’s work.
My problem is that, before using jitterbuffer in conference, I have a very good audio quality. But now ,with jitterbuffer, i have a very bad audio quality.

someone has already met this problem ?
Does jitterbuffer patch comes into conflict with the ilbc codec ?because it’s work well with G711.But I need ilbc codec.

thank you in advance.