This is the best app I've so far found for implementing the Replay Gain volume adjustment, which is far and away the best method of giving all your music tracks the same subjective volume adjustment. It doesn't mess with the internal dynamics of the track, but adjusts the overall volume of each track to match all your other tracks. This makes for much better sounding compilation and mixes. I mean, much much better. It's amazing what a difference this makes when listening. Absolutely indispensable. So good, in fact, that I actually shelled out the bucks to buy iVolume, which I rarely do, skinflint that I am.