Broadcasting old and new melody (2,3)
I believe the answer is:
on air
'broadcasting' is the definition.
(broadcasting on the air)
'old and new melody' is the wordplay.
'old' becomes 'o' (abbreviation).
'and' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'melody' becomes 'air' (synonyms).
'o'+'n'+'air'='ON-AIR'
(Other definitions for on air that I've seen before include "How one walks when elated" , "Cushioned" , "Radio show might be" , "very happily?" , "Walk in delight here" .)