Audio scrambling system using in-band carrier

Details Audio scrambling system using in-band carrier Audio scrambling system using in-band carrier

1990-04-26

1992-10-27

Swann, Tod R.

Cryptography

Key management

Having particular key generator

380 38, H04N 7167

Patent

active

051596318

ABSTRACT:
Audio signals are scrambled by single side band modulating with a modulation signal carrier having a frequency lying within the audio frequency band so that the signals are frequency translated upward. The scrambled audio signals are descrambled after broadcasting or recording/reproducing using a substantially identical modulation carrier signal to restore the original audio signals. Security is enhanced by varying the frequency of the modulation carrier signal in a pseudo random manner in response to start (ACLK) and rate (A0, A1) control signals. The control signals accompany the scrambled audio signals and are used during the descrambling process to aid in the generation of the descrambling carrier modulation signal. The frequency translation technique reduces the adverse effect of wow and flutter frequency fluctuations introduced during recording and reproduction of the audio signals (as compared to systems using frequency spectrum inversion), and also reduces the adverse affect of high frequency headroom crashing experienced in pre-emphasis broadcasting and equalizer recording applications.

REFERENCES:
patent: 3651268 (1972-03-01), Rivkin
patent: 3991271 (1976-11-01), Branscome et al.
patent: 4058677 (1977-11-01), Maitland et al.
patent: 4081832 (1978-03-01), Sherman
patent: 4244053 (1981-01-01), Clinch et al.
patent: 4276652 (1981-06-01), McCalmont et al.
patent: 4479226 (1984-10-01), Prabhu et al.
patent: 4636853 (1987-01-01), Forbes et al.
"Television and Audio Handbook for Technicians and Engineers" by K. Blair Benson et al., McGraw-Hill, Inc., 1990.

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