Nothing very loud to establish counterbalance (6)
I believe the answer is:
offset
'counterbalance' is the definition.
('offset' can be a synonym of 'counterbalance')
'nothing very loud to establish' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'very loud' becomes 'ff' (musical abbreviation).
'to establish' becomes 'set' (setting is a kind of establishing).
'o'+'ff'+'set'='OFFSET'
(Other definitions for offset that I've seen before include "make an effort" , "Compensate(d) for" , "Amount by which a thing is out of line" , "Place out of line" , "Counteract to compensate" .)