Encoding a hidden auxiliary channel onto a digital audio signal using psychoacoustic masking

We report on the development of a method of encoding an auxiliary channel onto a digital audio signal such that it is imperceptible to human observers. The encoding is accomplished by imposing slight and controlled changes on the phase spectrum of short-time signal windows. By employing principles of psychoacoustics the auxiliary channel is masked from human perception. Furthermore, the encoding and decoding are achieved via fast algorithms which allow real time processing. The method is applicable for any digitized audio signal containing voice, music, or other acoustic signals to be heard by humans. Possible signal sources include compact discs, digital television, digital radio, digital telephony, and any other source where an audio signal is in a digital format.