Horn sound in live recording (4)
I believe the answer is:
beep
'horn sound' is the definition.
(I've seen this in another clue)
'live recording' is the wordplay.
'live' becomes 'be' (synonyms).
'recording' becomes 'EP' (extended play vinyl record).
'be'+'ep'='BEEP'
'in' acts as a link.
(Other definitions for beep that I've seen before include "Electronic warning sound" , "Warning signal" , "Electronic noise" , "Alarming noise" , "Sound of a horn" .)