Video Disc: Mechanical Recording

The idea of storing a signal as a mechanical vibration is as old as Edison's original cylinder recorder, and of course have been used in audio records for almost as long. A needle or stylus follows a groove, and variations in the depth or width of the groove cause it to vibrate; these vibrations are turned back into the required electrical signal.

PhonoVision: The Baird Television Record

The very first video recording system of all was John Logie Baird's Television Record -also known as PhonoVision - which was first demonstrated in 1927 and developed through the 30's. This was a standard 78-RPM record, played on a normal gramophone which was hooked up to a Baird television. This was only possible because of the extremely low bandwidth of Baird's mechanical TV system, which ran at 12.5 frames per second, and used a mere 30 lines in each frame.

TV records were sold in the thirties by Selfridges in London, for seven shillings (35p) each, but Baird's television system was quickly superceded by the electronic scanning we use today and the TV record disappeared with it.

More information on PhonoVision can be found at another site. Ask at the enquiry desk.

TelDec / TeD

The UK firm Decca first demonstrated a prototype monochrome disc system in 1970. By 1973 they had been joined by the West German AEG Telefunken, and the format had been improved to give 10 minutes of colour pictures. In 1974 it was formally launched, as TelDec, with a six-disc autochanging player to give a total playing time of one hour.

The player used a ceramic stylus to pick up the signal from a spiral groove like a normal LP record. However, the 8 inch foil disc span at 1500 rpm, on a cushion of air rather than a turntable, and the grooves contained only vertical variations - LP grooves wiggle from side to side as well - which allowed them to be packed 13 times more tightly than on an audio record.

The signal was also frequency modulated, whereas an LP records the audio signal directly. Later models kept the discs in a protective sleeve, which did not have to be removed in order to play it, very much like a computer diskette.

The machines we re available in Germany, Switzerland and Sweden, for around £400 [1994: £2240], a colour TV costing around £260 at that time. Despite its high picture quality, TelDec didn't sell very well. In 1975 it was re-launched, now with stereo sound and re-named TeD, but appears to have sunk almost without trace. The only reference to the system in the UK was in 1983, when it was apparently being used to store medical records.

Visc

Matsushita (Panasonic) demonstrated another mechanical disc system, Visc, in 1978. This crammed an hour of colour video on to each side of a 12 inch vinyl record. The disc span at 500 rpm, rather than 1500, which means that three frames would have been recorded per revolution. This means that proper freeze-frame would not have been possible - the best that could be achieved would be to repeat a single revolution, eg three frames.

Visc was never launched, possibly due to the development by JVC, Matsushita's partner, of the more sophisticated SelectaVision / CED system described in a later exhibit.

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