Scrambling of analogue electrical signals
AssigneeBritish Broadcasting Corporation
InventorMichael A. Parker
Life of this patent
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Abstract
In a system in which an audio signal is scrambled by being divided into blocks each comprising a plurality of segments, and the segments are re-ordered within the blocks to provide the scrambled signal, the joins between the segments are required to be located at a descrambler. To enable the joins to be located, a framing sequence is added to the signal in synchronism with the segments and which consists of a low-level signal having a frequency spectrum which is substantially similar to the spectrum of the audio signal. Preferably a pseudo-random binary sequence is used having typically 200 to 500 bit periods per segment.
Claims7
A method of scrambling an analogue electrical input signal having a certain frequency spectrum in which:
- said signal is divided into segments;
- said segments are re-ordered to form a re-ordered signal;
- and
- a defined binary sequence having a frequency spectrum substantially similar to the said spectrum of said analogue electrical input signal is added to the re-ordered signal in synchronism with the segments.
Apparatus for scrambling an analogue electrical input signal having a certain frequency spectrum, the apparatus including;
- means for dividing said analogue electrical input signal into segments;
- means for re-ordering said segments to form a re-ordered signal;
- and
- means for adding to said re-ordered signal a defined binary sequence having a frequency spectrum substantially similar ot the said spectrum of said input signal in synchronism with the segments.
Dependencies are inferred from the claim text.