Make louder (7)
I believe the answer is:
amplify
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">make louder</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for amplify that I've seen before include "Increase in size, volume or significance" , "Make louder or fuller" , "Make fuller, increase the strength of" , "Expand" , "Make (signal) bigger" .)