Legal Question in Intellectual Property in California

Couldn't say for sure without knowing the contents of the instrument or at least some more background, but perhaps it would be helpful to know that a "derivative work" in copyright law is something that is a pretty close knock-off of someone else's copyrighted original, like a screenplay based on a novel, or photographs of someone's sculpture, or a performance of someone's song. (My apologies to experts in this field, for a somewhat imprecise definition).