DiscoVision and Other Ideas for Video Discs

Abstract

WHEN YOU HEAR THE TERM “DISCOVISION,” WHAT IMAGE COMES to mind? Is it John Travolta in that iconic pose on the dance floor with twinkling lights all around? Or is it some kind of augmented reality experience popular with those who are in the know?

Approximately 45 years ago, it was the name for one of a few similar technologies developed to bring prerecorded video to consumers’ homes to watch on their TVs. Assuming a format similar to a long-play record, engineers searched for ways to create a disc that easily could be inserted in a player and deliver combined video and audio tracks on a television for home entertainment. Early work considered many different means, such as magnetic, capacitive, mechanical, or optical. In practice, optical became the leading contender because it was intrinsically safe to the media when played, and it could operate under a wide range of temperature and vibration conditions. No matter how many times you played that Disney video for the kids, the disc would never wear out. But it was not the only approach developed.

You are probably thinking, “Isn't this what CDs and DVDs are today?” Some of the technology—including the ability to retrieve data from the surface of a flat disc using lasers—is similar, but these discs were analog and stored their data as optical features in either transparent or reflective surfaces that were then assembled directly into lines and frames of video (plus synchronized audio) in real time. This was accomplished with limited memory and none of the modern digital image-processing techniques we take for granted today.

This was the technical focus of the May 1976 issue of Information Display.¹ In his article, Kent D. Broadbent explained the ins and outs of the new system that was later to be commercialized by the Music Corporation of America (MCA) in 1978 and became what Pioneer sold as the “LaserDisc.”² The technology was based on an invention for a transparent video disc in 1963 by David Paul Gregg and James Russell and later was co-developed by MCA and Philips in the 1970s.

One side of a typical 12-inch disc initially stored 20–30 minutes of content (this later increased to 60 minutes). One TV frame was recorded per revolution of the disc, which spun at a relatively high rate of ∼1,800 revolutions per minute (RPM) for NTSC video playback (the American analog TV standard). Multiple electronics manufacturers made players for these discs. The formats evolved over time using varying rotational speeds and introducing digital audio tracks.

A master disc was produced on a metallized glass substrate, and information was recorded onto it by selectively melting the metallic coating with a laser (Fig. 1).² Mass-producing copies involved a photoresist-based printing process that was somewhat expensive for a consumer product.

RCA developed a similar rotating disc concept using the trade name “SelectaVison,” which used a mechanical stylus, somewhat like an audio record. Rather than converting mechanical movements into sound though, the stylus measured capacitance changes underneath the disc surface. Those signals were converted into video and audio content. The RCA format had four frames of content per rotation, and the disc speed was much slower at approximately 450 RPM. They also provided for a total of 30 minutes at first and then 60 minutes per side of content per disc. Fig. 2 shows a schematic of the stylus interaction with the disc.³ To reduce the risk of dirt entering the grooves, SelectaVision discs were sold in special carriers that would go directly into the player where the disc was extracted in a cleaner environment than the open air in one's house. The concept of using a guided stylus was promoted as an easy way to ensure proper reading of the data when the tracks were not perfectly concentric.

At this time, there also was the concept of a “film disc,” which was a transparent form of a video disc that could be played back in low resolution using an incandescent light source or a laser for higher bandwidth and a better signal-to-noise ratio. Jonathan A. Jerome discussed this in his article.⁴ Fig. 3 shows a transparent video disc holding 20 minutes of content. The clear spaces forming white slices are the frame boundaries. This system was expected to be useful for computer data storage as well as video. It had some advantages in the possible simplicity of playback systems compared with the other methods discussed.

As we know now, the timing for commercial analog video disc technology was not so good, as VHS and BetaMax video tape systems also were entering the market in the late 1970s. Consumers generally liked the ability to record their own programs as well as buy or rent prerecorded content. Videocassette players were more complex and had many drawbacks; however, volume drove down the costs, and they became easily affordable during the next decades.

Optical discs offered a higher bandwidth and a better-quality video experience than VHS and certainly found a niche audience of consumer enthusiasts. Pioneer continued to make LaserDisc players until July 2009.⁵

You can still find LaserDiscs and players for sale at some collectors’ events and online. If not for the eventual success of digital optical discs (CDs and DVDs) and now virtual recording and streaming technologies, we still might have rows of optical discs on our shelves sitting happily alongside our LP records and reels of old audiotapes. Well, some of us anyway.