Low brass instrument (4)
I believe the answer is:
tuba
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">low brass instrument</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 tuba that I've seen before include "Player" , "Big brass instrument" , "Musical instrument -- 5 (rev)" , "Producer of note" , "Noisy instrument" .)