Apple Final Cut Express 4 - Manual (Page 624)

624 Part VIII Audio Mixing
Until you create at least one audio level or pan keyframe in your audio clip, changes
you make affect the level or stereo placement of your entire clip. Although you need
two keyframes to do anything useful, once you set the first audio level or pan keyframe,
any changes you make to the keyframed levels anywhere else in the clip generate
additional keyframes.
To set a keyframe, do one of the following:
m Move the playhead in the Viewer to the place where you want to set a keyframe, then
click the Level or Pan Keyframe button.
m Select the Selection tool (or press A), then hold down the Option key and position the
pointer over the level overlay. The pointer turns into the Pen tool. Click a level overlay
with the Pen tool to add a keyframe at that point.
The keyframe appears as a small diamond on the overlay.
A keyframe appears at
the location of the
playhead.
Pen tool