Method and apparatus for scrambled pulse-code modulation transmission or recording

Claim 1

Method of processing video signals, for transmission or recording and reproduction in a single transmission or recording and reproduction channel, which signals have previously been encoded into a sequence of data words each of a first predetermined number (n) of pulse-code modulation (PCM) signal bits, which words sequentially correspond to periodic samples of said video signal obtained at successive instants definable by a sequence of clock pulses which also thereby define a sequence of intersample intervals, comprising the steps of: providing first and second timing signal sequences for respectively defining the beginning of first and second sets of alternate intersample intervals of said sequence of intersample intervals; inverting alternate words of said sequence in response to one of said timing signal sequences; interchanging a second predetermined number (m), less than said first predetermined number (n) and greater than one, of bits of each successive pair of words of said data word sequence in response to one of said timing signal sequences and thereby forming a pair of modified words from each said successive pair of words of said data word sequence, and transmitting a first one of each of said pair of modified words in response to said first timing signal sequence and transmitting a second one of each said pair of modified words in response to said second timing signal sequence immediately following the transmission of the first modified word of the same pair of modified words and thereby producing a continuous stream of modified words obtained at the same rate as said periodic samples to which said data words correspond, said first and said second modified words of each pair being consistently distinguished from each other in all pairs according to which modified word contains the uninverted bits which were not interchanged in the bit-interchange step.