Hi-fi system (6)
I believe the answer is:
stereo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">hi-fi system</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for stereo that I've seen before include "Musical sound with two speakers" , "With twin audio channels" , "Of sound equipment, having two speakers" , "A 19 player" , "Sound - not mono" .)