Observed how music is written (5)
I believe the answer is:
noted
'observed' is the definition.
('note' can be a synonym of 'observe')
'music is written' is the wordplay.
'music' becomes 'note' (synonyms).
'is written' becomes 'd' (I can't explain this - if you can you should believe this answer much more).
'note'+'d'='NOTED'
'how' is the link.
Can you help me to learn more?
(Other definitions for noted that I've seen before include "Observed - famous" , "Illustrious" , "Having renown" , "Significant" , "Recorded in writing" .)