High quality of sound after soprano departs (6)
I believe the answer is:
stoned
'high' is the definition.
(thesaurus)
'quality of sound after soprano departs' is the wordplay.
'quality of sound' becomes 'tone' (I've seen this before).
'after' says to put letters next to each other.
'soprano' becomes 's' (musical abbreviation).
'departs' becomes 'd' (common abbreviation e.g. train timetables).
'tone' put after 's' is 'stone'.
'stone'+'d'='STONED'
(Other definitions for stoned that I've seen before include "Doesn't (anag) - drunk" , "Slangily drunk or attacked with rocks" , "Like Olive perhaps" , "Slangily drunk or biblically executed" , "steeped in alcohol?" .)