Recording put in class (8)
I believe the answer is:
cassette
'recording' is the definition.
(thesaurus)
'put in class' is the wordplay.
'put' becomes 'set' (setting is a kind of putting).
'in' means one lot of letters goes inside another.
'class' becomes 'caste' (caste is a kind of class).
'set' put into 'caste' is 'CASSETTE'.
(Other definitions for cassette that I've seen before include "sealed plastic container" , "bit of outdated technology?" , "Recorder would accommodate this" , "It may contain film" , "sound equipment" .)