http://www.screencastingwizard.com/2012/11/28/levelator/ This video is a demonstration of the free software tool called Levelator.
Sometimes, when you're putting together an e-Learning project or even a simple audio/video blog post, you end up with funky sounding audio levels. Some parts of your clip seem louder, while others sound softer.
One way to fix this problem is to tweak your audio clips with an audio editor by using the Amplify effect to nudge affected sections up (or down) in an attempt to "level out" the entire clip. The thing is, that could be a lot of tweaking depending on the length of your project or the number of variations. That's where a free software tool called Levelator can help do the heavy lifting for you....
Via Ileane Smith