Additionally contributes to the general sound (4)
I believe the answer is:
also
'additionally' is the definition.
(I've seen this before)
'contributes to the general sound' is the wordplay.
'contributes to' says the answer is hidden in the clue (I've seen 'contributing to' mean this (the answer contributes to part of the clue )).
'ALSO' is hidden within 'general sound'.
(Other definitions for also that I've seen before include "As well, in addition" , "on top" , "into the bargain" , "'Besides, moreover (4)'" , "an indication of more to come" .)