Apple Final Cut Pro 5 - Manual (Page 645)

310 Part II Rough Editing
If the clip items you want to make into a stereo pair have different durations, the clip
items are trimmed to the region where they both overlap. The levels, pan settings, and
filters that were applied to the top clip are applied to both, and the clip attributes from
the bottom clip are ignored.
To separate a stereo pair:
1 Select a stereo clip item.
2 Do one of the following:
 Choose Modify > Stereo Pair, so that the menu item is unchecked.
 Press Option-L.
Volume level overlays
Two clips that are not a
stereo pair; length and
volume levels differ.
Before
Stereo pair indicators
Volume level overlay (the
same on both tracks)
Only overlapping parts of
the clips remain, and the
volume is copied from the
top clip to the bottom clip.
After