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/DECCA
Telefunken Fernseh- und Rundfunk GmbH, Germany
and
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.
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.
TeD video disc. Page 1: Early development. 1970 June 24.
TeD video disc. Page 2: Moving to the market. 1970 June 24.
PHILIPS/MCA
Philips Gloeilampenfabrieken, Netherlands
and
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
France
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
applications 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.
VIDEONICS
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.
MDR
Nürnberg-Reichelsdorf, West Germany
Paris, France
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.
RCA SELECTAVISION
Players were sold with these brands: Elmo, GEC McMichael,
Hitachi, J C Penney, RCA, Realistic, Sanyo, Sears, Toshiba, Wards, Zenith
Proto-video discs
Muybridge Zoöpraxography (1893)
Anthony Spiral (1898)
Urban Spirograph (1907-1915)
The quest for home video
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