OOC:
seems i don't understand how perform works in 5e. The skill states:
Performance. Your Charisma (Performance) check determines how well you can delight an audience with music, dance, acting, storytelling, or some other form of entertainment.
Nowhere does it say you have to select any specific discipline (or instrument).
My character took performance as a performance skill.
It does state that if you have tool proficiency with an instrument you add your proficiency modifier to your check.
The way this translates to me is:
Proficient in performance (but not instrument) = add proficiency modifier to performance check
Not proficient in performance (but proficient with an instrument) = add proficiency when using a specific instrument.
Proficient in performance (and proficient with an instrument) = add proficiency when using a specific instrument (proficiency doesn't stack)
Expertise in Performance =double proficiency when using performance.
Personally, I'd suggest, if proficient (or expertise) in the performance skill as well as the instrument, you should get advantage.
Otherwise, I don't understand why you would want to be proficient with an instrument 'and' proficient with the performance skill.
Or is it that being proficient with an instrument strument gives you proficiency in the perfoemance skill for that instrument...and then if you take proficiency in the proficiency skill you gain proficiency in the tool (instrument)...an either or scenario?