Note changed in quality (4)
I believe the answer is:
tone
'quality' is the definition.
(synonyms)
'note changed' is the wordplay.
'changed' indicates anagramming the letters.
'note' is an anagram of 'TONE'.
'in' acts as a link.
(Other definitions for tone that I've seen before include "Pitch of a voice" , "Quality of sound, etc" , "A pitch of note" , "Quality of a musical or vocal sound" , "accent" .)