Audition is explosive with ace group (7)
I believe the answer is:
hearing
'audition' is the definition.
(I know that audition can be written as hearing)
'explosive with ace group' is the wordplay.
'explosive' becomes 'he' (abbreviation for high explosive).
'with' is a charade indicator (letters next to each other).
'ace' becomes 'a' (abbreviation).
'group' becomes 'ring' (a ring is a criminal organisation).
'he'+'a'+'ring'='HEARING'
'is' acts as a link.
(Other definitions for hearing that I've seen before include "Perceiving sounds" , "Legal process" , "Judicial process" , "Audition - trial" , "Perceiving sound" .)