Of sound or hearing (5)
I believe the answer is:
audio
I believe this clue is a double definition.
'of sound' is the first definition.
(I've seen this before)
'hearing' is the second definition.
(thesaurus)
(Other definitions for audio that I've seen before include "Reproduction of recorded sound" , "Prefix indicating hearing or sound" , "Prefix indicating sound or word" , "shown in reproduction" , "Prefix signifying sound or hearing" .)