Non-stereo (4)
I believe the answer is:
mono
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">non-stereo</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for mono that I've seen before include "Single-speaker sound" , "Single-channel sound" , "Transmitting over one channel" , "Not stereo" .)