Broadcasting another perhaps about one (2,3,3)
I believe the answer is:
on the air
'broadcasting' is the definition.
(I've seen this in another clue)
'another perhaps about one' is the wordplay.
'perhaps' is an anagram indicator.
'about' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'another' is an anagram of 'onthear'.
'onthear' going around 'i' is 'ON THE AIR'.
(Other definitions for on the air that I've seen before include "radio listeners can now hear?" , "In the process of broadcasting, radio or TV" , "Anti-hero engaged in live broadcast" , "Broadcasting (hence audible)" .)