Apple Final Cut Pro 7 - Manual (Page 125)

Chapter 6 Working with Audio 125
Change Audio Levels over Time Jump In:
You can adjust a clip’s audio so that the audio level and pan change over time. To make
audio level or pan changes during a clip, you set keyframes at specific frames where
the audio should change. Next, you’ll use keyframes to edit the audio level values in a
clip to increase or decrease over time.
Increase in audio level