This illustrates a simple script I've made to reconvert mp3 files.

It does the following things:

1. Reconvert mp3s
2. Apply gain to mp3s
3. Sanitize tags and migrate them to specified version

This was to allow easier compatibility with all of the programs/devices when reading mp3 music. Specified formats can be tuned to needs, of course.
It is available through rsync at rsync://matrix.faskatech.net/mp3conv. It took me a while to rework all of the odds of bash scripting when it comes to paths containing spaces, but finally I made it. It is not perfectly working, as when re-executed multiple times creates spurious paths. Please beware that on the last step all of the tags get automatically stripped. That was to allow easier editing later, killing spurious entries and/or unwanted/unreadable tag fields. I suggest tag-editing through EasyTag (very versatile, easy and fast).