Regular pattern in sound (6)
I believe the answer is:
rhythm
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">regular pattern in sound</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 rhythm that I've seen before include "Measured beat" , "'I Got - - ' (Gershwin)" , "Regular beat in music" , "Recurring beat" , "Pulse, beat" .)