MUSE, HiVision, and the Laserdisc

	After the successful colour television broadcast of the 1964
 Tokyo Olympiad, NHK [Nippon Hyoso Kokkai, the Japanese state
 broadcaster] began to examine what the next likely development of
 television would be.  Their research suggested three major
 alterations would increase the value of television to the viewer:

1. A wider aspect ratio.
2. An increase in the total resolution of the picture.
3. High-fidelity multichannel sound.

	Other modifications, such as 3-D picture and interactivity,
 were examined and judged to be of little or no widespread interest. 
 Various other facts came out of the research; notably that only part
 of the increased resolution would go to making the picture visually
 sharper, as viewers would tend to reduce their viewing distances [in
 terms of screen heights] to increase the solid angle subtended by the
 image.
	Accordingly, in 1970 NHK opened discussions with Japanese
 electronics manufacturers concerning the development of the
 next-generation television system.  Work on what became known as
 HiVision advanced rapidly enough that in 1979 Matsushita Electric
 was able to offer a closed-circuit system scanning 30 frames per
 second, interlaced 2:1, with a resolution of 1125 scan lines [1035
 visible] and a video bandwidth of 30 MHz.  These specifications
 remained constant for the HiVision studio format.  There were,
 however, two important differences between this early implementation
 and the final product.  Firstly, the picture aspect ratio was 5:3, a
 screen shape for motion pictures more common in Japan and Europe than
 the United States; this was eventually supplanted by the 16:9 ratio
 proposed by Sarnoff Laboratories, striking a geometric mean between
 Academy and Cinemascope formats while approaching closely the 11:6
 VistaVision matte.  Secondly, what is more to our purpose, it
 employed a full-bandwidth composite format with the colour subcarrier
 at 24.3 MHz.
	For broadcasting purposes, a baseband signal more than seven
 times the bandwidth of NTSC posed severe problems of channel
 allocation even before audio transmission was considered.  Simply 
duplicating the existing service coverage might absorb all the
 spectrum available for television, and the immense investment in
 conventional equipment militated for the retention of NTSC broadcasts
 into the forseeable future.  Allocating new spectrum for terrestrial
 broadcasts or supplying every household with a separate CATV service
 were awkward options at best.  About this time, however, the advance
 of communications techniques opened the possibility of
 direct-broadcast satellite television service to the home.  After
 studies showed that the whole of the Home Islands could be blanketed
 by a single transponder [in practice, the greater part of the
 Republic of Korea is covered too, much to the annoyance of the
 authorities there, who do not allow television broadcasts after 7 pm
 and have little fondness for the Japanese anyway], this avenue was
 selected for delivery of the new service.
	Problems remained.  Chiefly, the power capabilities of
 available satellites were quite limited.  The dynamic range required
 for the successful decoding of a frequency-interleaved composite
 video signal was simply more than could be provided.  In Great
 Britain at the same time, Doctors Wyndham and Lucas were solving the
 very same problem for conventional PAL transmissions.  They separated
 the colour subcarrier from the luminance signal, concatenating and
 time-compressing the two components to fit in the ordinary line scan
 period.  Dispensing with frequency-interleave required, of course,
 additional bandwidth and extensive processing at transmitter and
 reciever, but the technique gave good results.  NHK engineers adopted
 this solution to one aspect of their transmission difficulties, but
 they were not out of the woods just yet.  Three 30 MHz picture
 components would require, of course, 90 MHz of bandwidth.  Filtering
 the two chroma components to half the luminance bandwidth still
 required 60; vertical subsampling, transmitting the two
 colour-difference terms in alternate lines, would occupy 45.  This
 was still far too much bandwidth to transmit via a standard 27 MHz
 satellite FM transponder, of the kind which ordinarily carried three
 NTSC channels at better than broadcast quality.  Having already made
 the commitment to radical signal-processing steps at the head end and
 the home, the interested parties decided to go for broke.
	The final delivery format is a masterwork of signal
 processing.  Known as MUSE, it is a complete audio-visual delivery
 format furnishing a creditable high-definition picture and
 multichannel digital sound within a comparatively narrow bandwidth. 
 As the system has a number of variants, an explanation of the broad
 features is in order.  Its most striking charactersitic is the
 Multiple Sub-Nyquist Encoding which forms the heart of the video
 processing, and supplies the acronym.  As the name will imply to the
 technically-minded, the video signal is broken up into frequency
 bands which are manipulated separately.  Filtering, time compression,
 and time expansion are used to allocate bandwidth preferentially to
 those bands which exhibit significant activity, while those which do
 not are decimated and left to be reconstructed by interpolation,
 reducing spatial redundancy.  Temporal redundancy is then reduced by
 decimation for subsequent interpolation of information carried over
 from previous fields.  Motion vecors are extracted to increase
 interpolation efficiency.  Audio is then added, in one of two
 Differential Pulse Code Modulation formats inserted into the vertical
 blanking interval of 45 lines per field.  DANCE [DPCM Audio Nearly
 instantaneously Compressed and Expanded] A-Mode provides four
 discrete channels, Left, Centre, Right, and Surround, at
 approximately FM radio quality from 15 bit, 32 kHz sampling; while
 DANCE B-Mode supplies Left and Right with a 48 kHz sampling frequency
 and a greater bit depth [16 or 20?].

	If the even and odd lines are considered as belonging to
 adjacent fields, the final packing structure is as follows:

LINES			CONTENTS
1-3			Vertical alignment signal
4-83			Audio
84-91			Audio and colour difference
92-1115			Luminance and colour difference
1116-1123			Luminance and control data
1124-1125			Control data

	The output signal provides a quoted static luminance bandwidth
 of 22 MHz and chroma of 7 MHz; for moving areas of the picture these
 figures fall to 14 and 3.5 [or better; this figure is apparently
 velocity- and hardware-dependent], which is largely masked by
 blurring in the camera and the eye.  This is equivalent to 675
 horizontal elements per picture height, or a picture element with
 dimensions roughly 1.5:1, comparable to what is provided by VHS tape
 or anamorphic 16:9 NTSC LaserDisc.  In other terms, the resolution
 matrix is 1035*1200.
	The above statements refer principally to MUSE-E, the standard
 which commenced trial broadcasts in 1988 and full-time operation in
 1992.  It is understood to have a transmitted bandwidth of 12 MHz
 using a 3-field sequence, which represents a bandwidth reduction of
 about 5:2 with respect to the output.  There are additional variants
 of the system.  MUSE-T is quoted at a 16.2 MHz bandwidth, and is said
 to employ only intrafield compression and have "no perceptible
 impairment" with respect to master-tape picture quality.  Narrow MUSE
 was developed for terrestrial broadcast in the United States,
 occupying only 6 MHz, and employs along with a 4-field sequence the
 curious expedient of subsampling the picture to 750 scan lines for
 transmission, justified by reference to the "Kell Factor" which
 supposedly reduces the percieved resolution of an interlaced video
 image by one third.  All of these formats employ the same decoder,
 along with a final one which is slightly more relevant to people
 outside Japan: MUSE HiVision LaserDisc.
	It is possible to increase the bandwidth of a conventional
 optical disc system in two ways: by reducing the reading laser
 wavelength, thus permitting a smaller spot to be detected; or by
 increasing the rotational speed and moving the pits past the laser at
 a greater rate.  At a high enough speed with a short enough
 wavelength, uncompressed HiVision signals could be accomodated, and
 it appears that Sony [with the HDL-2000] and Sanyo [HVL-BM2000] both
 have machines of rather limited utility which do just that at the
 cost of a short playing time.  The consumer market called for
 something less drastic.  Engineers at Sony, the lead corporation on
 this project, increased the rotational speed of the conventional
 LaserDisc by 50% to a maximum of 2700 RPM.  This boosted frequency
 response from about 12 MHz to 18.  Then a red laser was implemented
 to allow reduction of the track spacing so that the conventional
 playing times of 30 [in CAV mode] and 60 [CLV] minutes per side could
 be retained, increasing frequency response again to something like 21
 MHz.  Incidentally, the primary motive for ownership of MUSE LD
 players outside Japan is that the superior MTF of the optical section
 and lower noise floor of the signal-processing electronics give
 markedly better performance for playback of the standard NTSC discs
 with which virtually all are compatible.  Modulating a full MUSE-E
 signal on this bandwidth is a questionable proposition.  Reports
 suggest, however, that a subvariant of MUSE-E, perhaps using a
 4-field sampling sequence, is available with a bandwidth of 9 MHz,
 and in the absence of definitive information [such as a spectrum
 analyser connected to the MUSE output during playback would yield]
 this appears to be what was used on HiVision LD.  The
 field-interdependent structure of the picture signal and the offset
 vertical intervals suggest that CAV rotation format would be less
 useful, and still frames more troublesome, than on conventional LaserDisc.
	HiVision LD can also carry a Red Book type of PCM digital
 audio track, and chapter marks, time code, &c. probably must be
 provided in the subcode data.  A subcode stream is provided in the
 MUSE format [128 kbps for Narrow MUSE], but the detected MUSE signal
 is passed from the player to an outboard decoder without any feedback
 channel.  All the refinements applied to digital-audio LD including
 LD+G subtitles and dts 5.1 surround sound ought to be possible, but
 appear never to have been implemented.  While the picture quality is
 high, there are difficulties particularly with film-sourced material;
 quite possibly the "loop-back" of the fields during a 3:2 pulldown
 transfer disturbs the encoder parameters.  Certainly the encoder is
 the most important step in the MUSE chain, and the evolution of
 superior implementations must have contributed heavily to the
 improvement of picture quality reported on later titles.
	Unfortunately for the video enthusiast, the MUSE LD was not a
 commercially successful format.  Players and software were
 introduced at prohibitively high prices, media quality was as noted
 not necessarily stellar, and releases were sparse.  Only about 100
 titles, mainly a random selection of American movies, were released,
 the last in 1998.  Market penetration was slight, even counting the
 bizarre package deal sold as a virtual aquarium.  Player production
 continued for another four years to satisfy demand for the Ultimate
 LaserDisc Player in the form of Pioneer's immensely sophisticated
 HLD-X9, but that has ceased now.  With the gradual implementation of
 digital satellite and terrestrial broadcasting in Japan, and the
 introduction of prerecorded 12cm optical media supporting the
 1080*1920 pixel matrix digital high-definition format expected
 sometime next year, it would seem that MUSE in all its incarnations
 will soon be definitively obsolete.



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