Apple Final Cut Pro 7 - Manual (Page 937)

Finally, you’ll want to move the outside pair of each group of four keyframes outward a
bit, so the volume of the music doesn’t change too abruptly and startle the audience.
Less-steep slopes between keyframes result in more gradual fades from one audio level
to the next.
Adjust the slope of
the level change.
Example: Setting Subframe Audio Keyframes to Eliminate Clicks
Sometimes, when you find the perfect edit point for cutting a clip into your sequence,
you’ll notice a pop or click in the audio. This happens when you make a cut on an awkward
sample that just happens to occur at a frame boundary.
You can eliminate pops and clicks by setting keyframes for your audio levels to within
1/100 of a frame. Usually, changing an audio edit point by just a few hundredths of a
frame eliminates the clicking.
To set and adjust subframe audio level keyframes
1 Open the clip in the Viewer and click the Audio tab.
2 Move the playhead to the edit point that’s causing the click by pressing Shift-I or Shift-O,
or by using the Up Arrow and Down Arrow keys to move from one sequence edit point
to the next.
937 Chapter 57 Mixing Audio in the Timeline and Viewer