Helpful to the orchestra for example? (12)
I believe the answer is:
instrumental
'helpful' is the definition.
(similar in meaning)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for instrumental that I've seen before include "doing without singers" , "Acting as a means; piece of music without vocals" , "Helpful; composition" , "Like a musical piece - it's of help" , "Having some responsibility - not vocal" .)