iMovie includes an audio equalizer that lets you optimize the quality of sound in your video and audio clips. By adjusting its controls, you can affect the range of tones, from treble to bass, in any sound clip, including the audio recorded with a video clip, voiceovers, sound effects, and music.
The equalizer includes several preset options, such as Voice Enhance and Music Enhance, that make it easy to improve sound quality for specific uses.
To optimize sound quality:
Double-click a video clip or an audio clip (the colored bar that represents a voiceover, a sound effect, or music you’ve added to a clip, shown below) whose sound you want to optimize.
Click Audio at the top of the inspector that opens.
Select the Equalizer checkbox, and then do one of the following:
Choose a preset—Flat, Voice Enhance, Bass Boost, Treble Boost, and so on—from the pop-up menu.
Choose Custom from the pop-up menu, and then move the controls to modify the audio.
To preview changes to the selected clip, in the Project browser, move the playhead (the red vertical line) in front of the clip and then press the Space bar. Press it again to stop the preview.
You can start and stop the preview while the inspector is open, which makes it easy to make a change by moving the controls, preview it, and then adjust the controls and preview again until you’re satisfied with the result.
To restore audio to its original state at any time, even after you’ve closed and reopened the project, double-click the clip, click Audio at the top of the inspector, and then click “Revert to Original.”