Scrambling of signals by inversion
US4888799A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 3, 1986 |
| Grant date | Dec 19, 1989 |
| Priority date | — |
| Expiry date | Jan 3, 2006 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04K1/006
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
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. To mask the artifacts, track-and-hold circuitry is used to sample the unscrambled audio signal waveform level just prior to the artifact and hold this level throughout the short period when the artifact would occur.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.