Last Updated on April 16, 2017 by Dave Farquhar
A lot of people think audio doesn’t matter when they edit video. They’re wrong. If you notice the audio, something’s wrong.
An easy way to improve audio quality is to normalize it, which makes the volume more consistent. Windows users can do it with Normalizer, a GPL command-line utility (a GUI is available). Linux users can use Normalize.
Normalizing still won’t make bad audio sound good, but it will at least make bad audio sound better.

David Farquhar is a computer security professional, entrepreneur, and author. He has written professionally about computers since 1991, so he was writing about retro computers when they were still new. He has been working in IT professionally since 1994 and has specialized in vulnerability management since 2013. He holds Security+ and CISSP certifications. Today he blogs five times a week, mostly about retro computers and retro gaming covering the time period from 1975 to 2000.

Please may also want to look at Replay Gain for their music collections.
From what I can tell Normalize(r) recodes the audio which can add further noise to the signal. Replay Gain simply adds a tag to the files so that players adjust output levels. Thus you don’t lose any quality in recoding.
P.S. Would it be possible to add a “preview” button to comments?