Capital is eccentric, if loud (7)
I believe the answer is:
cardiff
'capital' is the definition.
(Cardiff is an example)
'eccentric if loud' is the wordplay.
'eccentric' becomes 'card' (card can mean an eccentric person).
'loud' becomes 'f' (short for forte - 'loud' in music).
'card'+'if'+'f'='CARDIFF'
'is' is the link.
(Other definitions for cardiff that I've seen before include "Welsh city" , "European capital, birthplace of Roald Dahl" , "Capital of Wales" , "Capital on the Taff" , "Welsh capital" .)