Apple Final Cut Pro 6 - Manual (Page 894)

Chapter 5 Using the Audio Mixer 109
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You can even adjust a fader to a new position while it is moving. For example, if a fader
on the control surface is slowly moving down from a 0 dB keyframe to a –60 dB keyframe,
you can move the motorized fader up to +12 dB, thereby creating new keyframes.
When you release the fader, it returns to its trajectory moving toward the
–60 dB keyframe.