From Ripple Training-

In this lesson you will get an in-depth look at FCP’s audio panning controls. Panning affects how sound from your timeline is routed to your speakers. You will also learn a ton of really useful “secrets” in this tutorial on how to work with keyframes.

Watch the complete video tutorial here.

Jon Chappell has a tutorial going over all the Final Cut Pro Audio filters. It describes each one in detail, giving tips on how they could be used. Read it here.