Just loud music (4)
I believe the answer is:
fair
'just' is the definition.
('fair' is associated in meaning with 'just')
'loud music' is the wordplay.
'loud' becomes 'f' (A musical term).
'music' becomes 'air' (air is a kind of music**).
'f'+'air'='FAIR'
(Other definitions for fair that I've seen before include "Impartial, so-so" , "Beautiful; exhibition" , "Considerable" , "Equitable, just (4)" , "Blonde; beautiful" .)