[Freeswitch-dev] VAD/ CNG question

I setup the following scenario: A calls FS, FS plays back a wav file. I turned on the following channel variables: rtp_enable_vad_in=true rtp_enable_vad_out=true My question is where in the code are these channel variables defined? Specifically, I'd like to modify the silence threshold that is used. For my purposes, I'd like to tune the threshold to something more agressive than the default value. I'm using g.711U codec. thanks, Andy