Adjust TX and RX gain (AsteriskNOW)

Hello,

I need help on adjusting TX and RX gain through my Analog Telephony card on my PBX server. the sound seems very low when i call through the dahdi channels.

I have the TDM808EF (Analog card) with 8 FXO modules.

I have AsteriskNOW on an CentOS Linux Operating System, with FreePBX 2.9.0.7 and Asterisk 1.8.4.4 .

Thank you for any assistance.

Nick