Audio on the timeline
When you click the Audio Mixer button 
on the timeline toolbar, you can access the audio levels and stereo or surround positioning of individual clips, and edit levels on the tracks using audio keyframing. The Master Volume for all timeline audio appears at the bottom the timeline header area.
on the timeline toolbar, you can access the audio levels and stereo or surround positioning of individual clips, and edit levels on the tracks using audio keyframing. The Master Volume for all timeline audio appears at the bottom the timeline header area.Surround sound
The Panner tool is fully surround-capable. For maximum flexibility, you can position any clip’s audio as desired in a two-dimensional listening field – from front to rear as well as left to right.
You can open the Panner popup by clicking the Panner tool button on audio track when Audio Mixer mode is active.
If you mix the audio for every clip as though for surround playback, you can still output a movie file with a stereo soundtrack using just the left-right balance information. If you further decide to output your project on DVD, the 5.1 surround-sound production will already be complete. For more information about the Panner tool, see The Panner.