A TV signal decoder including a pair of flipflops, for receiving vertical sync signals identified by a single vertical blanking pulse in field No. 1 and a pair of pulses in field No. 2, includes a time delay circuit for operating the second flipflop only in response to the two pulse field. The outputs of the flipflop are coupled to a pair of AND gates and are supplied with decoding information that is serially translated under control of the appropriate field signal for decoding the television signal. A counter identifies the horizontal line number and is coupled to a PROM where the decoding information is stored for a specific scrambling system. The PROM may be replaced to enable operation with a different scrambling system.

An audiovisual subscription system includes means for aperiodically inverting the lines of a transmitted video signal on a frame-by-frame basis and for decrypting encrypted PCM audio information which is transmitted along with the aperiodically inverted video information.

A video scrambling and descrambling system that produces color video that is difficult or annoying to watch by randomly switching the color components of a component or composite video. In the scrambling portion, component or composite video is decoded into a luminance component and its two color components. A random switching signal is generated to randomly switch the relationship of the color component signals. The randomly switched color component signals may be encoded together with the luminance signal to produce a component or composite video signal that is scrambled. The random switching signal may be transmitted as part of the encoded signal or through a separate data channel medium. A descrambling portion first separates the scrambled component or composite video signal into a luminance component and two scrambled color components. The random switching signal transmitted to the descrambler along with the scrambled video signal is used to restore the original relationship between the color component signals. The luminance component as well as the two descrambled color components are then encoded to produce a component or composite video with the relationship between the color components restored to their respective original positions in the video signal. The method may be used in various transmission and recording formats.

Apparatus for encoding and decoding information. Multiple scrambling techniques are provided to prevent unauthorized reception of a television picture signal. A first mode of scrambling provides for shifting randomly occurring horizontal synchronization pulses within each field of video signal producing horizontal as well as vertical instability. Video line inversion of selected lines within a field comprises a second mode of scrambling of the signal. A third mode of scrambling provides for amplitude shifting the television signal during selected portions of the signal which contains luminance and chrominance information following a line synchronization pulse.

An in-band television signal scrambling method and apparatus are disclosed which employ a scrambler which receives and scrambles a television signal and one or more descramblers for restoring the scrambled television signal to an unscrambled condition. A tier level encoding scheme is used to identify and render operative predetermined descramblers. The scrambler encodes tier level coding information in the form of whiter-than-white pulses on a scrambled television signal, these pulses being detected by the descramblers, with only those descramblers identified by the tier level coding information being rendered operative to unscramble the scrambled television signal. The descramblers preferably employ a plug-in module into which the tier level coding information assigned to a particular scrambler can be programmed. The scrambling operation may be accomplished by suppressing the amplitude of the horizontal synchronizing signals in a television signal, and generating timing pulses in the form of other whiter-than-white pulses in the scrambled television signal which cue the descramblers enabling them to reconstruct the suppressed amplitude horizontal synchronizing signals.