If you search for "normalize" you'll see some stuff about that package, which includes an XMMS plugin that deals with RVA2 tags and does dynamic renage compression (despite the name of the package; let's not go down the normalization isn't range compression rathole again; I know it isn't, you know it isn't, the name of the package is historical). The previous discussion should include a link, but if not, you can find a pointer on freshmeat.