Note varies in quality (4)
I believe the answer is:
tone
'quality' is the definition.
(I know that tone is a type of quality)
'note varies' is the wordplay.
'varies' is an anagram indicator.
'note' with letters rearranged gives 'TONE'.
'in' is the link.
(Other definitions for tone that I've seen before include "Colour quality; note" , "Note as in voice" , "accent" , "Quality or character of sound" , "Mood" .)