present the most popu- applicable primarily to studios converted for component working. lar approach, it is possible that sub-band coding, based on splitting Digital cassette recorders for use on composite signals (D2 format) the picture into different two dimensional frequency bands (sub- have also appeared. The increased packing density of metal particle bands) and encoding each one separately may give slightly better videotapes has led to the successful development of lower cost quality than equivalent DCT schemes, particularly for multi resolu- analogue component cassette recorders using half inch tape formats tion applications such as HDTV broadcasting. (M.II and Betacam-SP) suitable for both studio and field operation. During 1989, a further digital composite digital tape format (D3) was announced by Panasonic Broadcast (Matsushita) based on a 57.2.4.4 PAL plus half inch wide metal particle tape with a tape thickness of 10um using M.II (VHS) type cassettes but with thinner tape. The cassettes The possibility of developing for terrestrial and satellite broadcast- are substantially smaller than those of D1 or D2 for equal running ing an enhanced, compatible wide screen (16:9 aspect ratio) version time. In all three formats there are four digital (PCM) audio chan- of 625 line PAL came under investigation in Europe in the early nels plus analogue tracks for cueing and time code. 1990s by a consortium of major receiver manufacturers and a An analogue signal can be converted to digital form, processed number of broadcaster research organisations. Objectives include: and then reconverted to analogue form several times in tandem with 16:9 aspect ratio; freedom from PAL cross effects; improved resol- little visible degradation. However, if this tandem chain is extended ution; compatibility with normal PAL and recordable on standard too far it will tend to lead to a marked increase in the quantisation VCRs; a display compatible with HD-MAC/HDTV. Various noise caused by the use of a restricted number of amplitude leve