Add a very quiet finale (6)
I believe the answer is:
append
'add' is the definition.
('append' can be a synonym of 'add')
'a very quiet finale' is the wordplay.
'very quiet' becomes 'pp'.
'finale' becomes 'end' (I've seen this before).
'a'+'pp'+'end'='APPEND'
(Other definitions for append that I've seen before include "Add (to the bottom of a document)" , "Add on at the bottom - say signature" , "Adjoin" , "Add, annex" , "Add on, attach" .)