Method and apparatus for low cost audio scrambling and descrambl

Details Method and apparatus for low cost audio scrambling and descrambl Method and apparatus for low cost audio scrambling and descrambl

1993-12-14

1995-11-28

Cain, David C.

Cryptography

Key management

Having particular key generator

380 31, 380 38, 380 39, 380 40, H04N 7167

Patent

active

054715318

ABSTRACT:
Audio signals are descrambled by double sideband modulating the scrambled audio signal with a modulation carrier having a carrier frequency slightly above the highest audio signal present in the scrambled audio. This produces a double sideband signal that is passed through a low pass filter which in turn is modulated by a second carrier frequency lower than the first carrier signal by an amount equal to the offset spectrum of the original scrambled signal. The first low pass filter nulls out any residual carrier from the first modulator that results from the of intermodulation of the two modulation frequencies that would be audible at its descrambler output. The modulators used are low noise switch type modulators that improve the signal to noise ratio in the descrambled signal over the previously used linear modulators. The use of switch type modulators provides a lower cost device with improved performance. A companion scrambling device uses similar techniques to provide improved performance at a lower cost.

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patent: 5058159 (1991-10-01), Quan
patent: 5144666 (1992-09-01), Le Van Suu
patent: 5159631 (1992-10-01), Quan et al.

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