Broadcasting no new tune (2,3)
I believe the answer is:
on air
'broadcasting' is the definition.
(broadcasting on the air)
'no new tune' is the wordplay.
'no' becomes 'O' (resembles 0 - 'no' can mean 'zero').
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'tune' becomes 'air' (air can mean a piece of music).
'o'+'n'+'air'='ON-AIR'
(Other definitions for on air that I've seen before include "In the process of broadcasting - floating aloft?" , "very happily?" , "Walk in delight here" , "Broadcasting at this moment" , "Live broadcast" .)