Loud summer gala (8)
I believe the answer is:
festival
'gala' is the definition.
(I've seen this before)
'loud summer' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'summer' becomes 'estival' ('estival' means relating to the summer).
'f'+'estival'='FESTIVAL'
(Other definitions for festival that I've seen before include "Period for feasting and celebration" , "Traditionally time of celebration" , "Day set aside for celebration" , "Fair" , "Fete" .)