Deacetylates O-acetyl-ADP ribose to yield ADP-ribose and free acetate. Down-regulates ribonuclease 3 (RNase III) activity. Acts by interacting directly with the region of the ribonuclease that is required for dimerization/activation. 3''-O-acetyl-ADP-D-ribose + H2O = acetate + ADP-D-ribose + H(+) 2''-O-acetyl-ADP-D-ribose + H2O = acetate + ADP-D-ribose + H(+) Homodimer. Interacts with RNase III. Belongs to the YmdB family.