...
Depending on the signaling type, if you don't know about signaling type - read this FXS vs. FXO Signaling article first.
Then edit the "channel =>" line(s) in zapata.conf
...
Static can be caused by high system resources, see the article Why Am I Getting Alerts?
Electrical Grounding
Make sure a working molex (power) cable is connected to the analog card. The PBXtra must be powered down while this is performed.
Make sure the PBXtra is on a grounded electrical outlet.
...
Transcoding
Refer to the article on Transcoding Audio to troubleshoot transcoding