A bend sound belongs to either a slide or a bend.

When a bend sound is attached to a slide, the join is to table notation, since slide is a type of notation. The notation table notation_type field value is slide in this case.

When a bend sound is attached to a bend, the join is to table technical, since bend is a type of technical. The technical table technical_type field value is bend in this case.

Join field to the bend_sound record in each of these tables is bend_sound_id.