Video Disc Systems

 

This article was lifted from Television April 1980. However it has been edited in places by Radios-TV and images inserted by Radios-TV to help illustrate.

Introduction

Imagine yourself back in 1980, the home is awash with all the latest tele-visual home entertainment gizzmo’s, Colour television is a little over 10 years old and has rapidly matured. The VCR market launched just a few years prior is really starting to take off in a big way with more and more households taking the plunge be it via one of the many rental outlets or for the brave, an outright purchase.

A casual glance through any of the more popular TV journals could lead you to believe that a new dawn in TV is just around the corner – in the form of video discs. Indeed phrases like “early next year”, “cost equal to that of a good television set”, “on -going pilot market trial situation” are bandied about by the PR men with great zeal. Well, we shall see, remember the build up given to the Teldec video disc system some ten years ago, while Baird’s video disc system (Phonovision) was first shown in 1928. Both these systems were briefly on sale in the UK, but met with little success.

Philips have been pushing VLP600/700 (as shown) laserVision disc system for quite a few years (it was first unveiled in 1972), but it has yet to appear on the UK market: 1981 is the latest predicted year for a domestic market launch in the UK.

Philips LaserVision

So what is it then that’s so far prevented the video disc from making any real impact on the market, and what are the real advantages and possibilities of video disc systems? The quick answer to the first question is technical problems. To understand what these are and how they can be overcome, let’s look at some of the principles of operation that can be used for video disc systems.

Basic Disc Systems

The first video discs to appear on the market went on sale at Selfridge’s Oxford Street store in 1935 – at seven shillings each. They were intended for use with the Baird television system, i.e. the system was a low -definition one, with about six minutes per side from a 78 r.p.m. disc. Because of the very limited bandwidth, conventional disc cutting, pressing and playing techniques could be used – with a thorn needle! So much for history. Many new video disc techniques have been developed since the 1930s – in fact I’ve found reference to some forty different systems. The fundamental difference between the systems is the method of recording the video signal. There are four basic techniques, mechanical, capacitive, magnetic and optical. Each has advantages and disadvantages. Let’s look briefly at each. The first, historically, were mechanical arrangements we’ve already mentioned Baird’s system. By mechanical, we mean that the signal modulation is present in physical form in the disc’s groove, and is sensed by a pick-up which is in contact with the disc. Mechanical systems have the advantage of using relatively simple technology, and thus have a low initial cost.

The TeD or Teldec system, jointly developed by Decca in the UK and Telefunken in W.Germany, was shown in 1970 as a monochrome system and was up -graded to compatible colour in 1974. It never apeared on the domestic UK market, though it made a brief appearance in W. Germany. Apart from one institutional UK user, it’s totally vanished from the scene. The main technical features of the Teldec system were the use of f.m. for the recorded signal and the fact that the pickup remained at a fixed height, the flexible disc being brought up into contact with the pickup head by air pressure from beneath. The disc rotated at 1,500 r.p.m., i.e. 25 revolutions per second = two fields (one picture) per revolution. This provided a playing time of around ten minutes, the real disadvantage of the system (the picture quality was very good). Attempts at an autochange system to extend the playing time were reported, but never seem to have come to anything.

Capacitive recording

Is used by the RCA Selectavision system, the JVC Video High Density system and the little known Polish Fonica system. Of these three, only the RCA system seems anywhere near putting in a market appearance. Basically, the sound and vision signals are recorded as capacitance variations along the disc’s track. The disc has metal and plastic layers in order to provide the capacitive effect, and the signal is sensed by a capacitive pickup with a diamond and metal stylus. RCA are understood to have pressed several hundred thousand discs for laboratory and field trial use. They’ve also invested very heavily in developing the system.

Magnetic recording

is the only practical method of providing recording and playback on a single unit the other systems are designed for replay only. Magnetic disc recorders have been used by professional broadcasters for many years, and are a source of sports’ stills and action replays. The Ampex HS2000, one of the first disc recorders, continuously records, reads and re-records a magnetic disc. The process takes 45 seconds, so this is the maximum storage time. Fine for penalties and ski jumps, but not much use for general purposes. Only one magnetic disc system came anywhere near the domestic market MDR (Magnetic Disc Recorder), produced by a German and French company and first exhibited in 1974. This used a double -sided, 305mm. disc running at 156 r.p.m. to give a playing time of about twenty five minutes per side. Prices suggested in 1976 were £375 for the player and £5 per disc. The system never materialised however and seems to have vanished.

Optical

The final technique is to scan the disc optically, i.e. by means of a light beam. The signals are recorded in a form that modulates the light beam. This is the technique used by the only disc system to have been sold in fair quantity, the Philips/MCA VLP (Video Long Play) system, which uses a low -power helium -neon laser to scan the disc. The signals are recorded in the form of a series of very small pits which vary in length. The laser interprets this as a form of pulse position modulation. The pits are arranged in the form of a spiral track, with no mechanical contact between the disc and the laser. The laser head traverses the disc, and to ensure that it remains aligned with the recorded track an elaborate servo system is used. In fact there are three laser beams, two to provide the servo signals that keep the third, signal sensing beam correctly aligned with the track. An optical scanning system developed by Hitachi employs a 305mm. disc rotating at 6 r.p.m. This enables 54,000 frames of picture information (NTSC colour) to be stored, and is apparently intended as a stills store system. The sound, luminance and chrominance signals are recorded on the disc in the form of 1 mm. diameter holograms (a hologram is an interference pattern, producedby merging both halves of a laser beam, one direct from the laser and the other after reflection from the object). On playback, a low -power laser is used to scan these holograms from three angles. Laser systems have the potential to provide a record/playback system for the user, though little work on this seems to have been done. So much for the basic ways of putting video information on to a disc. Let’s now look in greater detail at some of the technical problems and the ways in which various firms have tackled them.

Markets

There are two basic video disc markets – domestic and business/educational. Each has its own requirements and  thus technical problems. The domestic market is primarilybased on the supply of feature movies. With this type of use you require a long playing time and stereo sound, but probably not a very great disc life – how often would you watch MCA Discovision number P10-521, “Saturday Night Fever”, even at $15.95?! What’s probably not required is still frame, slow and fast motion, search, frame by frame advance, etc. For business use however the disc would need to be employed as a rapid information retrieval system, and with each of the 50,000 odd frames storing a still or text page you require a very robust disc, with still frame, rapid access to any stored frame, frame by frame advance and slow and fast search facilities. At first sight it might appear that these two markets, with their different requirements, would lead to the emergence of two  incompatible disc systems. Some manufacturers in fact have opted for one market or the other, and have built suitable hardware. This however is a costly approach, and means you can aim at only part of the total market.

The approach adopted by Philips/MCA is to aim at satisfying both types of user. To get a still picture without using a digital frame store something too expensive for domestic use, at least for the present – the disc player has to be able to read the same picture frame continuously. It can do this only if each revolution of the disc plays back a single frame of picture. This occurs with a constant rotational speed of 1,500 r.p.m., as we’ve already seen, but is wasteful of disc space since the information is packed more densely at the centre of the disc
and less densedly at the outer edge. As a consequence, a playing time of only about thirty five minutes per side is possible. The arrangement also gives noiseless slow and fast motion however, by repeating or skipping individual frames. Extended Play Instead of packing the information on the disc in this rather wasteful way it can be packed at maximum density, i.e. each frame occupies the same track length at any point across the disc: this gives a playing time of fifty-five minutes per side (the Philips Extended Play system). It means however that the disc’s speed of rotation has to alter as the laser traverses the disc.

We get a longer playing time, but we lose the still frame and fast/slow motion facilities since each revolution towards the outer edge of the disc (the laser scans
from the centre outwards incidentally) will contain several frames instead of just one. But do you really need these facilities for home movies, i.e. domestic use? Philips have in effect developed two systems, one ideally suited to domestic use and the other for information retrieval. Cleverly however a single player meets both needs, playing either type of disc. It automatically checks which
type of disc has been inserted, and then functions accordingly. For information retrieval, each frame is individually “numbered” and can be called up by keying the appropriate frame number into a remote control unit. The average access time for any one frame is about three and a half seconds.

CHRONOLOGY OF VIDEO DEVELOPMENTS

  • 1928 Baird Phonovision system demonstrated.
  • 1935 Baird Radiovision discs on sale.
  • 1964 RCA First conceived in 1964, the CED system was widely seen as a technological success which was able to increase the density of a long-playing record by two orders of magnitude.
  • 1970 Teldec demonstrated, 5 mins monochrome.
  • 1972 EVR (electronic video recording – a TV set playback system using film storage) abandoned. Philips VCR launched
  • 1972 Philips VLP announced.
  • 1973 Teldec demonstrated, 10 mins colour.
  • 1974 Teldec launched on German market, with cross licencing agreement with Sanyo and King Records of Japan.
  • 1974 Philips VLP “hope to market this year”, and mass produce “within a few years”
  • 1975 MCA laser “Discovision” system abandoned in favour of joint development with Philips VLP.
  • 1975 Teldec renamed TeD: stereo sound added.
  • 1977 RCA presses 200,000 Selectavision test discs.
  • 1978 VLP/Discovision on trial sale in Atlanta, USA, player at £350, discs at £3 to £8.
  • 1979 Cross -patent agreement between Philips and other European, US and Japanese manufacturers concerning video discs.
  • 1981 17 years late, RCA launches CED selectavision, its too late. Sales for the system were nowhere near projected estimates. In the spring of 1984, RCA announced it was discontinuing player production, but continuing the production of videodiscs until 1986, losing an estimated $600 million in the process.
  • 1995 DVD developed
  • 1997 DVD comes to market
  • 2000 Laserdisc ceases
  • Yes there’s more but that’s where I will stop

RCA’s Selectavision System

RCA, with their Selectavision system, have gone the other way, opting for a relatively low -technology approach aimed at the domestic movie audience. Their investigations into video disc systems began in the 50s, and by 1978 had reached the stage where the player and disc specifications had been finalised and several hundred thousand test discs produced. The system’s launch on the US market is expected to be in early 1981. The system uses 300mm. discs running at 450 r.p.m., giving sixty minutes playing time per side. The colour signal, with stereo sound, is stored on the disc in the form of capacitance variations transverse slots of varying width and periodicity impressed in the bottom of the spiral groove.

The tip of the metal/diamond electrode stylus serves as a capacitance probe to recover the signal. The conductive surface of the disc acts as the other plate of the capacitor. The stylus tracks across the disc in the spiral groove as with a conventional audio LP. As the stylus is in contact with the disc, a layer of lubricant is added to reduce friction and extend both the disc and stylus life. The finished disc is packed in a cassette to provide protection – the player automatically removes the disc from its pack once this is posted into the player. Since no still or fast/slow motion is possible with the system, it’s not suitable for information retrieval.

Hitachi VIP201P C.E.D Player

Hitachi VIP202P C.E.D Player

Japanese Developments

The Japanese manufacturers have not been inactive in this field of course, and several systems have been announced at various times. The situation seems to have settled down somewhat recently however, with Sony joining forces with Philips to produce a common optical system and Matsushita and JVC agreeing to adopt JVC’s VHD disc system as a joint standard. This presumably means that Matsushita’s groove -guided conventional stylus system has now been scrapped. JVC’s grooveless, capacitance system is certainly the more sophisticated of the two. The smooth discs allow the pickup head to move freely across the surface, making still frame, fast and slow motion etc. facilities possible. The technical details are as yet somewhat obscure – even to JVC in the UK! It’s known however that each frame can be individually located, as with the Philips VLP system, and that stereo sound is available.

The disc itself has been refined, and now lives in a caddy which is posted into the player. JVC claim that conventional disc pressing techniques can be used to produce the discs, and this should help to keep the cost down. No date for a UK launch has so far been set, nor has any price been suggested.

VHD

Summary

The present position then seems to be that Philips are ahead with their high-technology VLP system, and having joined forces with Grundig and Sony could see their system adopted as an international standard. I recently had an opportunity to examine a Philips/MCA player purchased in the US, and was interested to note that many of the components are marked “made in Holland”. It seems that Magnavox (Philips’ US subsidiary) are assembling the players from kits of parts shipped in from Holland. It’s  rumoured incidentally that the relatively expensive helium –
neon laser may in future VLP players be replaced by a solid-state version. This would help in bringing the price down and make the player more robust. No definite date for the launch of the Philips system in the UK has been decided upon, but Philips are considering the use of the Mullard Blackburn factory as a disc pressing plant – it’s expected to be brought into operation later this
year. So VLP could well be in the shops here late next year. Selectavision is scheduled for nationwide distribution in the USA next year, and RCA hope to sell around 200,000 players at about £250 each during the first year. An impressive number of deals with software houses have already been signed, including Disney, 20th Century Fox, MGM, Rank and Paramount. No date for a UK launch has been suggested, and there are no plans yet for a PAL version of the player.

Finally

Well we know how it ll developed RCA took too long to release the CED videodisc system, developed in the 1960’s it too a whole 17 years before they got to market by which time, it was a waste of time VHS had dominated the market. It lasted all of six months after launch in the UK with just over 250 titles ( 1,700 in the U.S.A) and was gone by 1983 but discs continued until around 1986. This monumental failure resulting in the end of RCA.

Laserdiscs held a niche market for a while but ultimately DVD taking over before that too was superseded by HD-DVD and blue-ray with HD-DVD going the way of the dodo. DVD sales still continue to this very day.