Against tune being broadcast (2,3)
I believe the answer is:
on air
'being broadcast' is the definition.
(on air on radio or TV)
'against tune' is the wordplay.
'against' becomes 'on' (I've seen this in other clues).
'tune' becomes 'air' (air can mean a piece of music).
'on'+'air'='ON-AIR'
(Other definitions for on air that I've seen before include "Cushioned" , "Broadcasting live" , "If you're really happy, you'll float here" , "(Walking) elatedly" , "In the act of broadcasting" .)