How many files are you talking about? If you are looking at 12 or so MP3 files for a CD, the best way might be to bring those 12 MP3's (or wav files, preferably) end to end into a DAW (with a gap between). Then you can manually normalize them so they are approximately the same volume.

I haven't done this myself yet, but I will on my CD project. It is probably the best poor man's mastering you can do. You can add slight limiting and compression to the whole mix to give it a unified sound.


Now at bandcamp: Crows Say Vee-Eh @ bandcamp or soundcloud: Kevin @ soundcloud