'Album Artist' tags are stored inside mp3s and other music files. They denote the artist for a musical release, as distinct from artists for the tracks that constitute a release.
That sounds like a technicality, so when do Album Artist tags become useful? Consider compilation albums. Each track in a compilation album may have a different artist, but the album as a whole should be viewed as a 'Various Artists' album. Therefore, we can tag the album with an 'Album Artist' tag of "Various Artists".
This gives us a lot of flexibility; we can find all songs by a given artist whether on dedicated albums by that artist or as tracks on compilation albums. We can also find albums whose Album Artist tag is "Various artists", which would give us all compilation albums. Using Album Artist tags makes our music collection more navigable.
All this would be for naught if your music player of choice doesn't support Album Artist tags. Most do, but there are differences between them. Recall that Album Artist is a 'tag' written into a music file. These 'tags' are name value pairs similar to "albumname=Thriller". The name of the tags change depending on the player and the music file format. Here's a table of the tag field names that each music player reads from/writes to when concerned with Album Artist.
|ID3 v2 (MP3)||Vorbis Comment (FLAC and OGG)|
|WinAmp||TPE2||ALBUMARTIST or ALBUM ARTIST|
|Windows Media Player||TPE2||[not supported]|
|Squeezebox||TPE2||ALBUMARTIST, ALBUM ARTIST or MUSICBRAINZ_ALBUMARTIST|
|Foobar||ALBUM ARTIST||ALBUMARTIST, ALBUM ARTIST, MUSICBRAINZ_ALBUMARTIST|
|Sonos||TPE2||ALBUMARTIST or ALBUM ARTIST|
So it's not simple. Different file formats such as MP3 and FLAC store Album Artist in different ways, and even for a given format different players can work differently. Foobar's support for MP3, for instance, writes to the "ALBUM ARTIST" field while others write to the TPE2 field. Using the TPE2 field is arguably incorrect, because the TPE2 field was created to hold the performing band information. The source of some of these differences lie in the ambiguities arising from music tagging. While specifications exist for music tagging, they are not treated as 'de jure' formal specifications that must be abided. Rather, 'de facto' trends in tagging emerge which are backed one way or the other by the music players. Album Artist is an example of this. Music collectors and music software writers realised there was a need for a tag like Album Artist. Unfortunately, no de jure specifications define it. It was down to the software writers and the collectors themselves to define it in a de facto manner.
Now, the ambiguities of music tagging could have its own blog post (or nine!) so I'll leave it there for now. Suffice to say, the upshot for us as music fans, is that all this gives us a headache when we want to change music players. What's right for one player is not necessarily right for another.
Album Artist tags should be applied for all compilations that have different track artists. Otherwise, some music players will list each track artist and album name as a separate album. For these tracks, set the Album Artist to something like 'Various Artists' (or whatever is appropriate in your language) and apply this title consistently.
It's important that the album artist tag is kept the same for all tracks on an album. If there are even minor differences some music players will treat the two variations as different albums, and separate the tracks therein each album. That's little better than having normal track artists!
The best way to change these tags is to use a music tagger or use your music player. You will have to select all the tracks for a given album and find the option to change the Album Artist for all tracks. If using MP3 tagging software, refer to the table above to decide which tags names to set. Your tagger may obfuscate the underlying tag name that is being written to. If this is the case, you may have to do a little more research to ensure the tag name is correct.
Once the tagging is complete, typically you must tell your music player to 'rescan'. This makes the music player re-read your music files, picking up the change in Album Artist you applied earlier.
This is a lot of manual work, and it's something that needs to be done again and again as you add music. This is another area where rule based music management would be useful.
I hope this advice makes your music collection easier to navigate!
Thanks to °Simo° and greencandy8888 for the images above.