Exclude one sound singer (8)
I believe the answer is:
baritone
'singer' is the definition.
(I know that baritone is a type of singer)
'exclude one sound' is the wordplay.
'exclude' becomes 'bar' (synonyms).
'one' becomes 'i' (Roman numeral).
'sound' becomes 'tone' (tone is a kind of sound).
'bar'+'i'+'tone'='BARITONE'
(Other definitions for baritone that I've seen before include "Male singer looks odd in boater" , "solo voice" , "Adult male singing voice" , "Male voice with deep register" , "One who can sing" .)