Ducking Audio in Final Cut Pro X

FCPX makes it easy to selectively adjust the audio of a specific portion of a clip. You'll find this useful often, like when you need to remove a swear word or audio pop, or fade down a spot's background music when its voiceover starts. This article uses the Range Selection tool to very quickly adjust a clip portion's volume, but first, some basics:

If a video clip contains audio content, the audio waveform appears by default in the bottom half of the clip's silhouette in the Timeline.
By default, all audio tracks display a black line. This line, or envelope, represents the volume of that track's audio: the top of the bar is louder, the bottom of the bar is quieter.

Step-by-step instructions after the jump...

In this example, we'll use the Range Selection tool to fade down a loud portion of a generic audio track.

First, use the spring-loaded Range Selection tool (keyboard shortcut "R") to select the audio you'd like to lower. Press and hold the R key as you click and drag across the clip in the Timeline. A yellow range selection box appears as you drag. When you release the mouse and release the R key, FCPX automatically switches back to the Arrow Tool.
Now, adjust the audio levels in this range. If you prefer the mouse, click and drag the black line downward to reduce the volume. If you prefer the keyboard, use Control+Plus Key and Control+Minus Key to raise and lower the volume, respectively. Here, we've reduced the volume by 11dB.
If the small height of the waveform doesn't give you enough precision, you can increase the height by using the Clip Appearance dialog in the Timeline. Click the light-switch-shaped icon at the bottom right of the Timeline, and toggle between the graphical buttons to view the thumbnail/waveform display presets.
Look more closely at the audio ducking we created in the clip. Final Cut Pro has automatically faded the audio down at the beginning of the range and up at the end of the range. To adjust the duration of these fades, just click and drag the respective keyframes in the horizontal direction. For example, here we have made Final Cut spend more time fading down at the beginning of our ducked audio.
To adjust the volume in the ducked section, you could click and drag vertically on the clip's keyframes, but it's quicker to click and drag directly on the black volume envelope.

We spend lots of time on this and many other audio techniques in our Final Cut Pro X classes. Come join us in our Orlando classroom, or bring us out to your studio for fully customized, one-on-one training.