Apple Final Cut Express HD - Manual (Page 634)

634 Part VIII Audio Mixing
In the next example, all three audio tracks already have audio edited onto them, and
the audio channel 2 Source control is connected to track A3. After using the Voice Over
tool, a new track A4 is created, and the new audio clip is placed there.
If another audio clip is already present in the audio track below the track connected
to the audio channel 2 Source control, a new audio track is inserted below this track.
All previously existing audio tracks below this are moved down to accommodate the
new audio track.
Before
The newly recorded
audio clip
After