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.

Abstract: A system and method for generating a variable frequency sine wave carrier signal operates in response to a start signal and a rate signal. The system includes a first counter which drives a second counter via an EPROM; the second counter is clocked by the output of an oscillator. The output of the second counter is converted by filtering to the desired sine wave signal.