Ballad Liberace covered without rehearsal (2,3)

I believe the answer is:

ad lib

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'without rehearsal' is the definition.
I can't judge whether this defines the answer.

'ballad liberace covered' is the wordplay.
'covered' says the answer is hidden in the clue (the answer is covered up by the clue).
'AD-LIB' is hidden in the letters of 'ballad liberace'.

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(Other definitions for ad lib that I've seen before include "Improvise a speech" , "with no forethought" , "Addition to speech" , "Freely available" , "Spontaneously" .)

I've seen this clue in the Sydney Morning Herald.

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