Except for some notes of music (3)
I believe the answer is:
bar
'except for' is the definition.
(I've seen this in another clue)
'some notes of music' is the wordplay.
'some notes' becomes 'ba'.
'of music' becomes 'r' (I can't justify this - if you can you should believe this answer much more).
'ba'+'r'='BAR'
Can you help me to learn more?
(Other definitions for bar that I've seen before include "Batten" , "Public house" , "Saloon" , "an amount of pressure" , "A pub counter or iron rod" .)