Muffled (5)
I believe the answer is:
muted
'muffled' is the definition.
('mute' can be a synonym of 'muffle')
This is the entire clue.
(Other definitions for muted that I've seen before include "fitted with silencer" , "Faint" , "Not loud" , "Soft-pedalled" , "Muffled, subdued" .)