|The idea of storing a signal as a mechanical vibration is as old as Edison's original cylinder recorder, and of course has 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 converted directly into an electrical signal and hence into a sound wave.|
Ancient History: The Baird Television Record
Naturally, this well-known technique was tried for video, and in fact the first video format of all was the Baird Televison Record - also known as PhonoVision - which was first demonstrated by John Logie Baird in 1927.
|This was a standard 78-RPM record, intended to be played on a modified gramophone, which would be 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.|
Baird's Phonovision recorder
The camera was in the "shed" in the background; the record's rotation is driven by the shaft emerging from the hole, to keep it in synch with the camera's scanning disc
|TV records were sold in the 1930's by Selfridges in London, for seven shillings each -- the equivalent of about £10 today. Since Baird never seems to have produced a working player, and certainly never had one on sale, this was rather an odd idea; people would simply listen to the chirrup of the TV signal, and imagine the wonderous future it suggested.|
|By the late 1930s, Baird's mechanical television system had been improved to 240 lines, but other pioneers had developed an alternative sytem -- the electronic scanning system we use today. As soon as the public could see both side-by-side, the superiority of the 405-line electronic TV was apparent, and Baird's mechanical "televisor" was obsolete.The TV record disappeared with it, though apparently a few TV records did survive -- 11 are known to exist...|
|More information on PhonoVision and the history of Television can be found other sites: ask at the information desk.|
|The idea arose again during The First Videocassette Revolution; 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 on 8-inch flexible disks, which could be simply and cheaply stamped out. The TeD format was the only mechanical format which actually made it to market (and so the only one featured in this museum); it was demonstrated in 1970, as a monochrome system, then formally launched in 1974 after colour was added.
A prototype TED player;
the actual machine featured in this room is nothing like it!
|TED doesn't seem to have been a big success, perhaps because of the limited playing tim (although a version with automatic disc changing was apparently developed). The mechanical loading system was also a source of problems, with disks sometimes getting caught in the mechanism -- making TED the only disc format to have lacing problems! |
One source claims that only about 2000 were sold. In 1975 it was re-launched, now with stereo sound, but appears to have sunk almost without trace. The only recent reference to the system I have found was in 1983, when it was apparently being used in the UK to store medical records.
Matsushita (Panasonic) demonstrated another mechanical disc system, called Visc-O-Pac, in 1978. This crammed an hour of colour video on to each side of a 9 inch (230mm) vinyl record, using "hill-and-dale" recording like the earlier TeD system.
The disc span at a relatively slow speed (700 to 300 rpm CLV), in order to pack enough playing time in, but with more than one frame per revolution Visc would never have been able to support freeze frame or other trick play / random access features.
Visc was never launched; in 1980 JVC abandoned the system and threw themselves in with the VHD / AHD camp. The capacitive VHD system is described in another room.