Musical surge (9)
I believe the answer is:
crescendo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">musical surge</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 crescendo that I've seen before include "Conceders (anag.)" , "Gradual loudening" , "Growing louder (mus.)" , "Gradual increase in loudness, musically" , "climax" .)