mation when the source signal is applied to an appropriate output device, such as a speaker or a display...http://www.google.com/patents/US5940135?utm_source=gb-gplus-sharePatent US5940135 - Apparatus and method for encoding and decoding information in analog signalsAdvanced Patent SearchPublication numberUS5940135 APublication typeGrantApplication numberUS 08/858,562Publication dateAug 17, 1999Fi