A singer? Not so. I perform as a musician (10)
I believe the answer is:
bassoonist
'a musician' is the definition.
(I know that bassoonist is a type of musician)
'a singer? not so i perform' is the wordplay.
'a singer?' becomes 'bass' (bass is a kind of singer).
'perform' indicates anagramming the letters (I've seen 'performs' mean this).
'not'+'so'+'i'='notsoi'
'notsoi' anagrammed gives 'oonist'.
'bass'+'oonist'='BASSOONIST'
'as' acts as a link.
(Other definitions for bassoonist that I've seen before include "Woodwind player" , "Musician" .)