Apple's iMovie program assembles video clips into completed video projects viewable on a computer, burned to a DVD, or transferred to a mobile device, for example, an iPod. Voices in the video clip that are accompanied by background noise can be difficult to hear. You can reduce the level of background noise of a video clip in iMovie to enable the other audio to be more easily heard. The procedure will not physically alter the video clip, so you will be able to experiment with how much reduction you feel is required.
Double-click the icon of the hard drive that is on the Mac's desktop. Double-click the "Applications" folder inside the window that appears. Scroll down to "iMovie." Double-click the program to launch it.
Drag the video or audio clip that is to have its background noise reduced into the upper left side of the iMovie's main screen.
Double-click the audio or video clip picture that is on the program's main screen. Click the "Audio" tab at the top of the "Inspector" window that appears.
Select the "Reduce background noise by" checkbox. Drag the slider next to the checkbox to the right to increase the reduction value -- for example, until the number by the slider reads "68." Click the "OK" button to close the window.
Drag the red line at the bottom of the audio or video clip that is on the program's main screen all the way to the left. Press the "Space" bar on the keyboard to play the audio or video clip. Readjust the procedure with the slider if the amount of noise reduction is not to your liking.
Reducing the background noise by greater than 75% can cause video degradation.