Sound unit (7)
I believe the answer is:
decibel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sound unit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(decibel is a kind of sound unit)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for decibel that I've seen before include "Measure of noise intensity" , "Sound level unit" , "Noise unit" , "Unit relating to sound or power measurement" , "Measure of sound" .)