Automon, not mix the recorded channels, append them

Hello, I’m starting with asterisk, I have a Freepbx with Asterisk 1.4.24.
I had installed and configured all things and works great.
But when I use the automon, the WAV file, has first the caller channel and after the callee channel. I didn’t found anything about that in the forums.
This is a issue or I need to config some variables. Obviously I need a mixed WAV.
Thanks in advance