When creating the recording of the instrumentals of a song, should it be related to a recording of the song with the karaoke versions relationship or be related to the work itself as a recording with the instrumental attribute?
You should relate the instrumental recording to the original using the “karaoke version” relationship, as well as link the work to the instrumental recording (but do NOT use the “instrumental” attribute).
If that is so, when will the instrumental attribute be used?
Also, unrelated but what is the relationship for this scenario.
Artist A released a song in language X. Artist B did a piano cover of the song. Artist C translated the lyrics of the song into language Y and used the piano cover by artist B as the instrumental of his cover.
I would create a work crediting Artist A connected to Artist A’s recording. Connect that work to Artist B’s recording with Instrumental and Cover checked.
Create a new work crediting Artist A with a credit for Artist C as translator. Link it to the original work with a Based On relationship, then connect that work to Artist C’s recording.
An instrumental is not the same thing as a karaoke but unfortunately many releases show karaoke called as instrumental.
Karaoke is the same recording except that they have removed the vocal track from the mix. This is why it is a recording to recording relationship, it is like a remix. Only the accompaniment (backing tracks) remain. No more melody.
An instrumental has the melody part played by instrument. Here you will link to the work as instrumental, which also means that the lyrics of the work are not rendered in the recording.
On another note, is there a vocal only relationship should there be one? Like, instead of just the instruments being played, only the voice is in the recording.
That would be covered by the relationships on the recording. After all, someone singing an a-capella version of a song is still singing the notes.