An encoder transforms at least a portion of a signal, counts the resulting transform coefficients having a zero value, and encodes the signal with the zero count. A decoder decodes the signal in order to recover the zero count. The decoder may also determine its own zero count of the signal as received...http://www.google.com/patents/US20040170381?utm_source=gb-gplus-sharePatent US20040170381 - Detection of signal modifications in audio streams with embedded code
