Sip jitter buffer

HI,
I have a problem…

I have in sip_general_custom.conf

this…

to enable jitter buffer

jbenable=yes
jbforce=yes
jitterbuffer=yes
dropcount=5
maxjitterbuffer=250
maxexcessbuffer=350

however I have tried this…

;Enable Jitter Settings
jitterbuffers=4
jbenable=yes
jbforce=no
jbimpl=fixed
;jbimpl=adaptive
jbmaxsize=500
jbresyncthreshold=100
jblog=yes
;tos=0x18

Question 1. Which is better ? -
Question 2. How do I look at the jitterbuffer log ? - I have used sip debu but cannot even see jitter buffer mentioned…

Any help greatly appreciated…