from http://bugs.musicbrainz.org/ticket/1552

There is a cool utility called mp3gain that is also opensource that would be ideal to include in mbtagger - in fact it's about the only feature keeping me from using mbtagger exclusively.

Mp3gain applies a standard gain level to each file - default is 89db but I typically use 93db. Have this user defined standard level applied by mbtagger at the same time as tagging/renaming, etc. would be greatly appreciated.

It appears we do have a couple of ReplayGain plugins, but nothing that works for all formats or all OSes.