Maybe bass part loud one needed at the start (3)
I believe the answer is:
fin
'maybe bass part' is the definition.
(part of a fish eg a bass)
'loud one needed at the start' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'one' becomes 'i' (Roman numeral).
'at the start' suggests taking the first letters.
The first letter of 'needed' is 'n'.
'f'+'i'+'n'='FIN'
(Other definitions for fin that I've seen before include "For movement and balance in fish" , "Fish propeller; end (Fr.)" , "Aerodynamic surface" , "Found on a fish" , "Swimmer" .)