Abstract: A method for encoding and decoding digital signals, particularly audio signals, by using multiple reference vectors from a codebook and adaptively updating the codebook. The reference vectors from the codebook are combined, using a mathematical combination function, to achieve a synthesized vector that most closely matches the digital signal. The encoded signal consists of the mathematical combination function coefficients and the memory addresses of the reference vectors from the codebook used to achieve the synthesized vector. The encoded signal is decoded by separating the coefficients and the addresses and using a reverse combination procedure to reproduce the synthesized vector. Finally, the synthesized vector is stored in the codebook, by overwriting the oldest data, to adaptively update the codebook.

Abstract: The present invention is directed to an inversion scrambler and unscrambler having pseudo-randomly controlled polarity-reversing switches to invert and re-invert, respectively, an audio signal so as to restrict the intelligent dissemination of the audio signal. To improve security of the scrambled signal, the audio signal is concealed prior to scrambling. Concealment includes clamping the original audio signal to a predetermined value and optionally offsetting this clamped signal prior to scrambling. The concealed signal is scrambled by inverting contiguous portions of the signal at pseudo-random intervals, accomplished by a polarity-reversing switching network controlled by a pseudo-random code generator. Upon unscrambling, artifacts will appear at the inversion points of the unscrambling signal, due to bandwidth limitations inherent in any transmission path.