You can make your audio more dynamic in Final Cut Pro by panning sound effects from the left speaker to the right from within the Viewer Window.
A sound effect, such as a passing car panning from the left speaker to the right, can add another dimension to your project and lessen the flatness of canned sound effects.
Before you try this, keep in mind that you only need a mono clip to perform this effect, so if you have a stereo pair, unlink the two and delete one of the tracks.
1 Double click on the audio clip to load it into the viewer.
2 Click on the channel tab in the Viewer Window.
3 Option click on the purple audio spread overlay in order to get the pen tool to create keyframes and drag the points of the line so that it looks like the diagram below. When you begin to move the purple overly you will see a pink line underneath it. It helps if you think of it in this way: think of anything above the pink line as being the right channel and anything below as being the left channel.
Now the audio in this clip will pass from the left speak through the right when played.