The Collaborative International Dictionary of English v.0.48:

Unmuffle \Un*muf"fle\, v. t. [1st pref. un- + muffle.]
   [1913 Webster]
   1. To take a covering from, as the face; to uncover.
      [1913 Webster]

   2. To remove the muffling of, as a drum.
      [1913 Webster]