I've tried that approach, but I find they aren't all that effective as the perceived volume levels end up being too varied between songs and it still does not combat against ambient noise such as would be found in a car which would tend to drown out quieter parts of songs. The purpose of such a processor is to reduce dynamic range in a controlled way to provide a consistent sound across sources, but also to avoid getting blasted away when you crank the volume to hear quiter parts which inevitably are followed by substanially louder parts. MP3gain and similar approaches do not combat this. I use Breakaway quite a bit with Pandora which I obviously could not use an ID3 tag normalizer with anyway.

It's not necessarily for serious listening; it's for casual listening, background music, mobile audio, television, etc.

Stu