Broadcasting old and new song (2,3)
I believe the answer is:
on air
'broadcasting' 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' is a charade indicator (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 "Broadcasting at this moment" , "Broadcasting studio sign" , "(Walking) elatedly" , "If you're really happy, you'll float here" , "Broadcasting live" .)