The quest for home video
Video discs: the view from the 70s
This page was originally compiled for a booklet produced in connection with the Video Disc 77 conference, held in London in November 1977. It has been changed from present to past tense but otherwise remains the same.
Telefunken Fernseh- und Rundfunk GmbH, Germany
Decca Record, London
TeD had the distinction of being the first video disc to reach the consumer market. First in West Germany in March 1975 and subsequently in Austria, Switzerland and Sweden, where it was been aimed more at the institutional buyer.
TeD video disc. Page 1: Early development
It was a purely mechanical system. A floppy plastic disc, containing a hill-and-dale cut spiral groove, rotated at 1,500 rpm on an air cushion generated by the disc's rotation. A diamond stylus in a piezo-electric pick-up functioned as a transducer, converting variations in pressure between the disc and the head into an electronic signal. The disc surface was therefore sensitive and was enclosed in an envelope which was fed into the player.
A 'select' button could be pressed for browsing; freeze frames were possible and a further refinement was the facility to repeat two-second segments at will.
Playing time was limited to 10 minutes—widely regarded as TeD's major drawback—but the size of the disc (210mm diameter) allowed direct pressing into magazines or newspapers, a possibility experimented with by one German publisher, although never developed commercially. Another drawback was that the programme master had to be film, preferably 35mm, and was transferred to disc at only 25 times real time. It was impossible to monitor the mastering process by visual display.
Software was steadily being developed, with arguably insufficient imagination, by a number of companies. Labels in the TeD Promotion Consortium included Decca, Telefunken, Ullstein AV, Videophon, UFA/ATE and Teldec Intertel. In Japan, Sanyo took up licences to manufacture players for the NTSC standard.
. 1970 June 24.
TeD video disc. Page 2: Moving to the market
. 1970 June 24.
Philips Gloeilampenfabrieken, Netherlands
MCA Disco-Vision, USA
The separate Philips VLP and MCA Disco-Vision were so similar in principle that it was inevitable that the standards-and compatibility-conscious Dutch company should form an alliance. On paper it looked like a world-beating combination, especially as Philips had a domestic consumer marketing expertise perhaps not even matched by RCA, Decca or Telefunken among other runners in the race and MCA had an impressive quantity of readily available (but not overly inspiring) software. The chicken and egg co-existed almost equally.
Apart from occasional joint technical announcements—Philips manufacturing the players, using its Magnavox subsidiary for US production—MCA made the promotional running. By 1977, the system appeared ready to go into production.
The metalised, reflecting disc—rigid or floppy—contains a continuous spiral track composed of minute pits. A laser beam directed onto the track is reflected back along the light path, having been modulated by the pits which contain the encoded information. A beam splitter directs the returned light to a photodiode detector for signal processing. For NTSC the disc rotates at 1,800rpm (÷60 seconds = 30 = frame standard) and at 1,500rpm for PAL and SECAM. Each revolution produces one frame and each frame can carry a numerical identification permitting any one of the 54,000 frames to be recalled and frozen simply by keying the relevant number on a keypad. Slow motion, reverse action and 'browsing' are also possible.
Philips said the HeNe laser assembly would cost around $10 in mass production and that players would cost $400-$500 at launch date, with discs at $2-$10 each retail, depending on programming.
Recording was in real time and replication was by pressing in PVC from stampers made from the master. After pressing, the discs were coated with metal and a transparent protective layer. Dust or dirt which gathered on the disc surface did not affect quality as it was out of focus.
Each company had, of course, been working on educational/industrial versions of the disc system independently. MCA took this rather more seriously than Philips, the latter having its eye firmly on the consumer market.
THOMSON CSF/THOMSON BRANDT
In many respects the twin Thomson disc systems—CSF was responsible for the institutional model and Brandt for the consumer version—were the same as the Philips/MCA system and considerable consultation took place during the mid 1970s towards a common standard. Collaboration with Zenith effectively came to an end when the latter withdrew from disc development.
During 1976, however, Thomson CSF diverged from the common design in two important respects. First a new, softer disc surface made it necessary to enclose the disc in a 'drawer' inside a plastic protection jacket. The whole package, confusingly known as a 'cassette', was inserted in the player and the outer jacket withdrawn. The disc was then lifted off the drawer (which remains in the machine throughout the playing time) into the playing position by air pressure. The 1.1mm thick discs were transmissively read by laser light using an astigmatic sensor and a vertical servo stabiliser and air blow system. Post-pressing coating stages were thus eliminated and cheaper player optics were claimed to be achieved as a result.
The cassetted discs were intended for more expensive pplications and the same type of disc, but without the protection, for throwaway purposes such as magazine inserts.
The second development, not explained in technical detail, was a method of compressing the audio signal so that up to 20 seconds of sound could accompany a single frame of picture.
RCA Government and Commercial Systems
Moorestown, New Jersey, USA
The RCA system employed a grooved disc with positive stylus tracking, which eliminated the need for expensive servo loops. Second, the stylus used, which incorporated a metal electrode to achieve the capacitance pick-up from the disc, was cheaper to manufacture than a HeNe laser assembly. In the player, only this pick-up was a non-standard component.
The 305mm disc was made of PVC which, after pressing, was coated with metal and dielectric layers. Information was recorded as slots of varying width and spacing in the bottom of the groove. Signals were derived from the capacitance between the metal on the disc and at the tip of the stylus. A system called 'buried subcarrier colour encoding' combined chrominance and luminance information.
A copper-coated aluminium master was mechanically cut with a spiral groove of trapezoidal cross-section, then coated with an electron beam sensitive material. While rotating on a turntable in a vacuum chamber, the disc was bombarded with a microscopically focused modulated electron stream which produces the required exposure. Those parts struck by the beam were removed during processing, after which electroless plating and further build-up by electroplating produced a negative master. Electroplating was then used on the negative to produce a positive 'mother' from which stampers were made by electroplating.
Each metal master could yield 10 mothers, which in turn could produce 10 stampers each, which were good for 1,250 pressings—making a total of 125,000 copies from one original master. Recording speed was gradually increased until it reached real time.
One drawback of the system was that the slower speed—450rpm, required to maintain relative stability—means that four frames were recorded per revolution, eliminating the possibility of freeze frame capability. Playing time per side was 30 minutes and both sides could be used. An 'armstretcher' device was used to correct speed variation by moving the arm backwards or forwards parallel to the groove—back to speed up, forwards to slow down.
RCA had another problem: it had no software of its own. This was overcome in two ways: by buying up old movies—acquired at not inconsiderable cost—and self-improvement films, and by trying to interest potential licensees.
Santa Clara, California, USA
The Videotron video disc was developed by a now defunct subsidiary of Videonics—i/o Metrics. At the time the parent company took over the rights to the system in mid 1977, there was 'only five per cent of the way to go'.
It was a laser-based system employing a 3mW helium-neon (HeNe) laser source to record FM analogue signals in the form of a spiral track on a 330mm diameter disc. i/o Metrics had not extensively investigated holographic recording. Flyback (vertical retraces) appeared as two dark bands of approximately 10° spaced 180° apart on the disc.
The disc was made of standard photographic materials and was processed in ordinary photographic chemicals—a process claimed to require minimal expertise—with a total dry-to-dry time of 10 minutes. Replication was by photographic contact printing. The major limiting factor of the recording process was the wavelength of the light used, as i/o Metrics made recordings considerably less thick than the emulsion. Centre-to-centre track spacing in excess of 500/mm can vary, giving disc densities up to 50,000 frames at one micron spacing. For data applications, discrete concentric circular tracks could be recorded rather than a continuous spiral track.
The company claimed that the photographic system was 'a natural choice' for small runs (less than 1,000 copies).
The player did not need to be level but could operate at even extreme angles approaching the vertical. Replay was achieved with a miniature 13 watt incandescent light bulb shining through the disc and the beam being focused by a microscope objective and a moveable mirror onto an avalanche photodiode video detector.
Applications envisaged by i/o Metrics, apart from domestic entertainment and general information, included audio recording, computer peripheral storage/retrieval and graphic data storage.
The recording unit was expected to cost less than $30,000, the player under $200 and the discs about 20 cents each plus programme costs. Retail price of $5 per disc was quoted.
Nürnberg-Reichelsdorf, West Germany
MDR (Magnetic Disc Recording) first attracted attention at the Vidcom exhibition in September 1974. Potentially it could have been a major system—if of relatively limited application—in that it was the only one with user-record capability. On the other hand, vacillations over the launch tended to discredit the system and leave the impression that either the backers are not yet satisfied with the commercial prospects or the system was fundamentally unsound.
Originally intended to operate at 78rpm on modified audio disc reproducers, the speed had to be doubled to 156rpm. The 305mm disc itself was rigid and coated with a fine grain magnetic substance jointly developed with BASF. The outer area of the disc surface was impressed with a continuous spiral groove which guided a stylus on the record arm. At the other (inner) end of a bar attached at right angles to the end of the arm was the magnetic record/pick-up head which was in contact with the smooth disc surface. Disc life was claimed to be in excess of 300 plays.
Both sides of the disc could be used, with a playing time of 20-25 minutes per side. Although recordings could be made in real time (a distinct advantage over some other approaches) all copies had to be made individually in the same way (a distinct disadvantage) although a multiple bank slave copying unit was clearly feasible. In terms of viability and cost, MDR was thus more akin to videocassette systems than video discs and for most purposes could be regarded as such.
Players were sold with these brands: Elmo, GEC McMichael, Hitachi, J C Penney, RCA, Realistic, Sanyo, Sears, Toshiba, Wards, Zenith
The quest for home video