[HELP] How setup the jitterbuffer?

I have an Asterisk PBX for make calls through IAX protocol. If I make calls with remote clients over internet, the quality of voice is orribile. So I sutup the jitterbuffer for improve the voice in this way:

iax.conf

[general]

jitterbuffer=yes
dropcount=10
maxjitterbuffer=500
maxexccessbuffer=100

Now the voice quality is better, but still no fantastic. The valeus that I’ve assigned to dropcount, maxjitterbuffer, etc. are right?

There are other ways to improve the quality of IAX channell?