Two-channel sound (6)
I believe the answer is:
stereo
'two-channel sound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stereo that I've seen before include "One might play record" , "Audio system, hi-fi" , "Of sound equipment, having two speakers" , "Sound transmission from two sources through two channels" , "With twin audio channels" .)