Interest in a fine female voice (6)
I believe the answer is:
affair
'interest' is the definition.
(affair is a kind of interest)
'in a fine female voice' is the wordplay.
'in' is an insertion indicator.
'a fine' becomes 'af' (I've seen this in other clues).
'female' becomes 'f' (abbreviation).
'voice' becomes 'air' (I've seen this before).
'af' enclosing 'f' is 'aff'.
'aff'+'air'='AFFAIR'
(Other definitions for affair that I've seen before include "River dam" , "Extramarital activity" , "Concern -- extramarital relationship" , "Raffia (anag)" , "Vaguely specified concern" .)