Instrument: gong ringing out at first (4)
I believe the answer is:
oboe
'instrument' is the definition.
(type of musical instrument)
'gong ringing out at first' is the wordplay.
'gong' becomes 'obe' (Order of the British Empire award or 'gong').
'ringing' means one lot of letters goes inside another.
'at first' says to take the initial letters.
The initial letter of 'out' is 'o'.
'obe' placed around 'o' is 'OBOE'.
(Other definitions for oboe that I've seen before include "Source of music" , "Orchestral piece" , "source of notes" , "Instrument used in 1d" , "Reed instrument" .)