Channel quality indexing and reverse indexing is described. One embodiment includes decreasing a skew rate at the rising andor falling edges of the gate signal to reduce the effects of data signal errors. The encryption method can select from a plurality of encryption algorithms. The sound mask is used in a sound box for obtaining a width sound field and a good distinguishing ability of sound source. The method includes: adding a database change to a top of a queue; and starting a non-active transaction service thread conditioned upon less than a predetermined maximum number of transaction service threads being present.