Telecast's sound portion (5)
I believe the answer is:
audio
'telecast's sound portion' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for audio that I've seen before include "Prefix indicating sound or word" , "Prefix indicating hearing or sound" , "Reproduced sound" , "Sound, as opposed to vision" , "Recording of acoustic signals" .)