New tune by Oscar being broadcast (2,3)
I believe the answer is:
on air
'being broadcast' is the definition.
(on air on radio or TV)
'new tune by oscar' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'tune' becomes 'air' (air can mean a piece of music).
'by' means one lot of letters go next to another.
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'n'+'air'='nair'
'nair' put after 'o' is 'ON-AIR'.
(Other definitions for on air that I've seen before include "Live broadcast" , "very happily?" , "In the act of broadcasting" , "If you're really happy, you'll float here" , "In the process of broadcasting - floating aloft?" .)