Note duplicated - thats only fair (4)
I believe the answer is:
soso
'only fair' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'note duplicated' is the wordplay.
'note' becomes 'so' (musical note).
'duplicated' becomes 'so' (I can't explain this - if you can you should believe this answer much more).
'so'+'so'='SOSO'
'thats' acts as a link.
Can you help me to learn more?
(Other definitions for soso that I've seen before include "Indifferent" , "mediocre" .)