Judge a musical instrument (8)
I believe the answer is:
recorder
This clue is a double definition.
'judge' is the first definition.
(historical type of judge)
'a musical instrument' is the second definition.
(recorder is a kind of musical instrument)
(Other definitions for recorder that I've seen before include "Musical instrument or note-taker" , "sound device" , "Judge; woodwind instrument" , "Judge - musical instrument" , "The one who takes notes and a tubular wind instrument" .)