Apple Final Cut Express 4 - Manual (Page 454)

454 Part VI Rough Editing
3 Set up a split edit in the Canvas or Timeline at the place where you want your source
clip to appear.
4 Drag the clip in the Viewer to the Overwrite section of the Edit Overlay in the Canvas.
The resulting edit looks like this:
Split edit with audio
preceding video
Audio precedes the
video, and begins at
the split audio In point.
Video begins at the
split video In point.