I just finished running my 6000+ mp3s through MP3Gain and am very happy with the results. It is a nifty program that adjusts the volume of all the mp3s to be about the same. This allows you to have a playlist that includes stuff from the 70s and the 00s without constantly having to change the volume so playback isn’t too loud or too soft. MP3Gain itself is a compromise between normalizing the mp3 before compression, which irrevocably changes the file, and programs like ReplayGain and Apple’s SoundCheck that store a volume level in the file comments. The problem with the first method is you can’t get back the original volume without re-encoding, and the problem with the second is that your playback programs have to support it. ITunes/iPod doesn’t support ReplayGain, and I don’t trust iTunes enough to let it change my files, so until now I have just been manually adjusting the volume a lot. MP3Gain changes the volume level in the file, but not any of the actual audio data. It also writes an ape tag with the original levels so you can change it back at any time unless you strip off the tag. I am finding a lot of cool songs/albums in my collection I didn’t really pay much attention to before because they were too soft to grab my attention. I am still going to keep an un-modified backup for a few weeks in case I run across any problems, but I don’t expect any.