@Bob Delbridge posted:
Having used 1/2 plywood myself, I would recommend using 3/4", I think that alone would help deaden the sound. If you do use 1/2", get extra hold-down brackets to hold it down to the Mianne framework, I had some warpage in my plywood and needed a dozen or so extra brackets.
I used 1/2" Baltic Birch, and there is zero warping in mine. I didn't use any of the hold-down brackets, we shot power staples into every support at 6" spacing. There's no vibration against the the benchwork, and zero warping with Baltic Birch. FWIW, at the time, Baltic Birch was not much more than regular sanded plywood, but it's a much better product.