Old and new song being broadcast (2,3)
I believe the answer is:
on air
'being broadcast' is the definition.
(I've seen this before)
'old and new song' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'and' says to put letters next to each other.
'new' becomes 'n'.
'song' becomes 'air' (I've seen this before).
'o'+'n'+'air'='ON AIR'
(Other definitions for on air that I've seen before include "In the process of broadcasting - floating aloft?" , "In the process of broadcasting on radio or TV" , "now showing" , "In the act of broadcasting" , "Cushioned" .)