Dynamic audio scrambling system
US4636853A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 21, 1983 |
| Grant date | Jan 13, 1987 |
| Priority date | — |
| Expiry date | Dec 21, 2003 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N7/167
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A multi-mode audio scrambling system includes an all-pass filter and a 90 degree phase shift circuit for supplying balanced modulators with 90 degree phase displaced audio information and 90 degree phase displaced carriers derived from the horizontal line frequency of a television receiver for producing a single sideband, suppressed carrier audio spectrum. A plurality of offset frequencies are derived from the horizontal line frequency and are used to further modulate the resultant signal to produce a single sideband displaced audio spectrum. A logic circuit selects the offset frequency (mode) in response to vertical interval signals, video inversion signals and audio tone or data signals. The final output is thus scrambled in different modes with different offset frequencies. A complementary unscrambling system is also described.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.