Approval going up, by the sound of it (6)
I believe the answer is:
assent
'approval' is the definition.
(I've seen this before)
'going up by the sound of it' is the wordplay.
'going up' becomes 'ascent' (I've seen this before).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'ascent' is a homophone of 'ASSENT'.
(Other definitions for assent that I've seen before include "Expression of agreement" , "Accede, agree" , "Permission" , "Agree - concede" , "Agree, acquiesce" .)