Muffled, subdued (5)
I believe the answer is:
muted
This clue is a double definition.
'muffled' is the first definition.
(I know that muffled can be written as muted)
'subdued' is the second definition.
(both can mean restrained or subtle)
(Other definitions for muted that I've seen before include "In music, with sound deadened or muffled" , "low-key" , "Hushed or stifled" , "Of great weight" , "Softened (of sound or colour)" .)