Note very loud Scene VI set out to provide potency (13)
I believe the answer is:
effectiveness
'potency' is the definition.
('effectiveness' can be a synonym of 'potency')
'note very loud scene vi set out' is the wordplay.
'note' becomes 'e' (musical note**).
'very loud' becomes 'ff' (musical abbreviation).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'scene'+'vi'+'set'='sceneviset'
'sceneviset' anagrammed gives 'ectiveness'.
'e'+'ff'+'ectiveness'='EFFECTIVENESS'
'to provide' acts as a link.
(Other definitions for effectiveness that I've seen before include "Capability" , "Potency" , "Power to achieve results" .)