Broadcast of choir? It's extremely notable (8)
I believe the answer is:
historic
'extremely notable' is the definition.
(notable in history)
'broadcast of choir? it's' is the wordplay.
'broadcast of' indicates an anagram (I've seen 'broadcast' mean this (letters scattered or cast around)).
'choir'+'its'='choirits'
'choirits' anagrammed gives 'HISTORIC'.
(Other definitions for historic that I've seen before include "Pertaining to what is important in the past" , "Epoch-making" , "Landmark; famous" , "Redolent of past glories" , "Momentous, noteworthy" .)