The process control unit of a microcomputer controls a decoder to decode an input signal, and acquires the voice format information of an input signal. One exemplary embodiment of the method comprises locating a first portion of the text that has a spatial frequency greater than a first preselected value. The thin layer permits the etching gas introduced to the cavity to decrease the overall etchant recombination rate within the cavity and thus, increase the etching rate of the sacrificial material within the cavity. The implantable medical device includes a cover coupled to edges of the housing defining the opening to substantially close the opening.