Decca, Telefunken and Panasonic all made mechanical video discs long after Baird had given up.
In the late 1960s and early 1970s Telefunken worked with British Decca on a mechanical groove-in-stylus video disc system called TeD (Television Electronic Disc). Teldec’s TeD was an updated version of the Baird system. Teldec engineers questioned the assumption that it was impossible to record colour video bandwidths (3MHz or more) on an audio disc. They spun the disc at high speed (1500 rpm) so that the short wavelength signals were stretched sufficiently for the plastics material of the disc to be able to store them.
But to get more than a few seconds playing time, the snake-like grooves on the disc had to be packed so close that they crashed into each other.
So Teldec’s clever engineers went back to Edison’s original sound recording system which used vertical, hill-and-dale modulation. In this way the grooves could be packed very tightly together, and give around 10 minutes from an 8in disc.
They used a flimsy plastic foil disc floating on air, with a piezo-electric pick-up and stylus shaped like the prow of a boat. The stylus skated along the groove, covering several undulations at a time, while its trailing edge transmitted a shock wave to the piezo transducer every time it passed over an undulation.
Teldec’s laboratory at Finchley in North London produced a working system that was ready for demonstration at the Berlin Radio Show in 1971. TeD was finally offered for sale on the Continent in the spring of 1975. Picture quality was pretty poor and Philips killed the idea stone dead by demonstrating the first optical video disc, Laservision, later called LaserDisc.
In 1978 Matsushita (Technics/Panasonic) re-invented TeD as a 12in rigid LP disc called Visc. This achieved the apparently impossible: an hour of colour TV on each side. But the groove pitch was 2.3 microns, around 1/25th the pitch for a conventional LP. No pressing plant could have produced the discs.
Matsushita dropped Visc, and temporarily backed the ill-fated VHD video disc system developed by its subsidiary JVC. But optical discs won the day.
Both Decca and Telkefunken hit financial problems but Telefunken could not bear to let all the work done on TeD go to waste. At the Audio Engineering Society Convention in New York, in November 1979, Telefunken unveiled a digital audio version, called Mini Disc.
MD was rigid, and housed in a protective caddy. The 13.5cms disc rotated at 250rpm and stored an hour of stereo on each side. Sampling was at 48KHz (higher than CD at 44.1KHz) but used 14-bit linear coding (compared to CD’s 16-bit linear). A 3in Micro version of Mini Disc gave 10 minutes per side.
In June 1980 Telefunken demonstrated MD to a committee of Japanese manufactures in Tokyo. Storage density was increased over conventional LPs by a factor of 1,000. The groove pitch was 1.66 microns, virtually the same as the optical track on a CD.
The player was a work of mechanical genius, tracking the disc with a force 50 times less than a