About call process ( no ring back tone)


Im using PIAF on my system. But any way with piaf i have a issue with no audio problem. Which is until call get answer i cant hear other party ringing or recordings. Im using polarity reversal for answer detection. so Untill call get answer i cant hear any audio feed. That mean asterisk not set up the audio path untill call get answer. Please anyone tell me in asterisk which part Or which configuration file handle this process.