Singer excluding one musical sound (8)
I believe the answer is:
baritone
'singer' is the definition.
(I know that baritone is a type of singer)
'excluding one musical sound' is the wordplay.
'excluding' becomes 'bar' (bar can mean excluding or except).
'one' becomes 'i' (Roman numeral).
'musical sound' becomes 'tone' (I've seen this in another clue).
'bar'+'i'+'tone'='BARITONE'
(Other definitions for baritone that I've seen before include "Second lowest male singing voice" , "Male singer between tenor and bass" , "Male singer looks odd in boater" , "One who can sing" , "solo voice" .)