Voice last part of play, not loudly (6)
I believe the answer is:
active
'voice' is the definition.
(I've seen this before)
'last part of play not loudly' is the wordplay.
'last part of play' becomes 'actfive'.
'not' is a deletion indicator.
'loudly' becomes 'f' (A musical term).
'actfive' with 'f' taken away is 'ACTIVE'.
(Other definitions for active that I've seen before include "Dynamic, functioning" , "kind of voice" , "Busy, not idle" , "Engaged, not idle" , "Industrious" .)