A duo, worried about one sound (5)
I believe the answer is:
audio
'sound' is the definition.
(audio means sound)
'a duo worried about one' is the wordplay.
'worried' indicates anagramming the letters (worry can mean to interfere with or disturb).
'about' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'duo' is an anagram of 'udo'.
'udo' placed around 'i' is 'udio'.
'a'+'udio'='AUDIO'
(Other definitions for audio that I've seen before include "TV sound" , "in the sound department?" , "Television sound" , "shown in reproduction" , "Sound broadcast" .)