Nerve : how a small Kentucky town led the fight to safely dismantle the world’s chemical weapons / a film by Ben Evans & the Kentucky Environmental foundation ; with music by Ben Sollee. (OCLC #937869675)

Which relationship designator should be used for the composer/performer of original music for a film, so often expressed in the credits as “music by”? I included that version in the Creation/Production Credits Note:

508 00 ǂa Directed and produced by Ben Evans; music by Ben Sollee.

But am a little bit nervous about my relationship designators for the authorized access point:

700 1_ ǂa Sollee, Ben, ǂe composer (expression), ǂe instrumentalist.

RDA I.3.1 defines composer (expression) as “A person … contributing to an expression by adding music to a work that originally lacked it, by composing new music to substitute for the original music, or by composing new music to supplement the existing music.” which seems accurate, but a bit off. Similar designators seem to refer specifically to musical works.