| Before you fade out the Bumper Sirens clip using keyframes, you should trim any blank space from the end of the clip. If you look carefully at the end of the Bumper Sirens waveform in the Audio Editor, you'll see a straight, horizontal line. A flat line in an audio waveform means the same thing as a flat line on a heart monitor: dead silence. So let's trim off the right edge of the clip. There are two methods for trimming clips in the Audio Editor: You can drag the edges of the green bar at the top of the editor, or you can use the handy In and Out value sliders. 
For this exercise, let's just drag the right edge of the clip (the green bar) to trim the clip. We'll set a marker first, to use as a guide for the trimming operation. 1. | In the Audio Editor, move the playhead to 4;00. Press M to set a marker at the playhead position.
A red marker appears on the clip. If a clip is selected when you press M, the marker appears on the clip, rather than on the timecode ruler.
| 2. | Move the pointer to the right edge of the clip (the green bar) in the Audio Editor until the pointer becomes a Trim tool.
| 3. | Drag the right edge of the clip toward the left, to the red marker on the clip.
The marker disappears because it has also been trimmed. That's okaythe marker served its purpose.
Now you can keyframe the last second of the clip and know that you'll be keyframing the portion of the clip that has audio, instead of silence.
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Keyframing on the Level Curve Let's try a different keyframing method to fade out the level at the end of the clip. Instead of using the keyframe pop-up menu to set keyframes, let's set them directly on the Level curve. How? Easy; just double-click the curve where you want to set a keyframe. You can also drag a keyframe to a new value. 1. | In the Audio Editor, move the playhead to 3;00.
| 2. | Double-click the Level curve at the playhead position to set a new keyframe.
You don't have to move the playhead to set a keyframe. This time, you'll set one without using the playhead as a guide.
| 3. | Double-click the Level curve near the end of the clip to set the last keyframe.
TIP Try not to set a keyframe too close to the edge of a clip, or it will be difficult to grab and move. You can always drag a keyframe to the edge of a clip once you've created the keyframe. | 4. | Drag the new keyframe at the end of the clip downward to a level of 96 dB.
| 5. | Press Cmd-S to save your progress.
| 6. | Press Cmd-9 to close the Audio Editor.
| 7. | Press the spacebar to see and hear the finished project in the Canvas, sirens and all.
The Level values for the Bumper Sirens clip on the Audio tab change to reflect the new keyframed values of the Level curve.
| 8. | Choose File > Close to close the project.
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Congratulations! You just created an audio fade-in and fade-out by keyframing the Level parameters in the Audio Editor. |
