How to Improve the Sound in an iMovie '11 Video
On your Mac, you can tweak the audio in your video so that the sound remains consistent from one scene to the next. Bummer — the sound in one video clip is barely above a whisper, whereas in another, you must turn down the volume. Adjusting the audio to give priority to the sound you want to be heard is known as ducking audio. Follow these steps:
Start by selecting a clip in the timeline.
Click the Adjust button on the toolbar.
Click the Volume button, and choose Auto.
iMovie analyzes and automatically enhances the sound in the given clip.
If you want to lower the volume of other clips at the same time, select the check box provided for that purpose. You can drag a slider to set the levels relative to the volume of the clip you've selected. Why would you do this? Perhaps you've recorded a voiceover and want iMovie to lower the music playing in another clip while the voiceover plays.
Repeat this exercise as needed in other clips.
You can always restore the volume to its original level by clicking the Undo button (it has a small curved arrow on it) or by choosing Edit→Undo Auto Loudness. Still another option: Press cmd+Z.
Now suppose that you want to lower the background noise in a clip but not alter the overall volume of the clip. You know, a plane flies overhead, someone in another room sneezes, whatever. Here's what you do:
Select your clip and click Adjust.
Select the Noise Reduction and Equalizer button.
Select the Reduce Background Noise check box.
Drag a slider to adjust how much the background distraction ought to be reduced.
If you click the Equalizer, by the way, you can apply other audio settings. You can enhance voice or music, reduce humming, and boost or reduce treble or bass, for example.