A singer to object to one wrong note (8)
I believe the answer is:
baritone
'a singer' is the definition.
(I know that baritone is a type of singer)
'object to one wrong note' is the wordplay.
'object' becomes 'bar' (bar is a kind of object).
'to one' becomes 'i' (Roman numeral).
'wrong' indicates an anagram.
'note' with letters rearranged gives 'tone'.
'bar'+'i'+'tone'='BARITONE'
'to' acts as a link.
(Other definitions for baritone that I've seen before include "Second lowest male singing voice" , "Male voice with deep register" , "Male singer looks odd in boater" , "solo voice" , "Adult male singing voice" .)