MusicBrainz’s Picard Tagger knows about the »Artist Sort Name« from the MusicBrainz database (i.e., »Zappa, Frank« instead of »Frank Zappa«).
It stores this this artist sort name in ARTISTSORT vor Vorbis Comments (FLAC, OGG), in TSOP for ID3v2.4 tags, and in XSOP for ID3v2.3 tags. iTunes 8 stores this field always as TSOP, even in ID3v2.3.
Mp3tag (fortunately) allows the use of TSOP in ID3v2.3 (called PERFORMERSORTORDER), though one might see it as »somehow illegal« since it’s not the ID3v2.3 specs. Then again, artist sort order was totally neclected in ID3v2.3, so everybody came up with a different solution (instead of probably just using a TXXX type field for that). Sorting artists is needed, after all, and not everyone can use ID3v2.4, for miscellaneous resons.
I’m not aware of any software that directly supports using XSOP (it’s an »experimental« tag), whereas we have more and more software respecting TSOP in ID3v2.3, due to iTunes doing it.
So I would very much like to be able to convert my MP3s that have XSOP set by Picard to using TSOP instead, to be compatible to iTunes and Logitech’s SqueezeCenter.
Unfortunately, Mp3tag does neither show nor edit the XSOP tag. Could we please have support for this tag, be it only to read/display it and then save as TSOP again?
It might be shown as a separate, but since normally no file would have both XSOP and TSOP, it might also be safe to read both XSOP and TSOP into PERFORMERSORTORDER for ID3v2.3. Then it would have to be rewritten as TSOP of course, and XSOP thrown away. Don’t know if everyone would like that. Anyway, XSOP would probably only used in an action to format TSOP and write it out again.