ansmitted on terrestrial channels. intercity/satellite distribution) is being investigated for both con- The original MUSE system permits the broadcasting of tribution and distribution circuits and possibly for broadcast dis- 1125/60/2:1 HDTV programmes in a single 12GHz DBS satellite tribution. Techniques include: sample rate reduction (reducing the channel, compressing the signal into a base bandwidth of 8.1MHz sample rate to the minimum value possible within the quality by multiple sub sampling and includes techniques for motion com- objective); discrete cosine transform (DCT) which is similar to the pensation, quasi constant luminance principles and non linear em- discrete Fourier transform with a block of N samples transformed phasis with a four field cycle. MUSE-T is a related system for the to give N coefficients, representing the amplitude of specific pat- distribution of HDTV programmes to broadcasters via communica- terns within the block and subsequently transformed back in the tion satellites, employing 2 field cycle sub sampling for motion decoder to give the original N samples (effective because the ma- resolution improvement. It has a 16.2MHz signal bandwidth requir- jority of coefficients have an amplitude close to zero); variable ing an FM channel of approximately 50MHz. NHK has also pro- length coding in which the number of bits assigned to a given 57/12 Video transmission quantised value depends on its probability; temporal prediction By 1987 digital cassette broadcast videotape recorders, based on modes which take advantage of the similarity of one picture to the EBU/SMPTE D1 digital component format, had reached the another; video framing in which all the information relevant to the market place, making possible all digital production centres. Such video signal is multiplexed together before being written into a machines can produce more than 20 generations of tape without buffer store. noticeable degradation, but represent a relatively high cost system Although DCT based coding techniques re