Such a note can't be forced (7)
I believe the answer is:
natural
'such a note' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for natural that I've seen before include "Unrefined person" , "Unaffected, normal in manner" , "Not disguised" , "Not man-made; off-white" , "Normal; not sharp or flat" .)