Video: Laserdisc Introduction

Laserdisc

A laserdisc is a play only, 12-inch (typical, there is also a 8-inch, known as a laserdisc single) diameter double-sided optical disc capable of 425 lines of NTSC video resolution used for playing back video and sound from a player which output to a television.

Laserdisc is a dramatic improvement over videotape, yet somehow it never caught on beyond a small niche of consumers. This can be attributed to a few factors: the large size and weight of the discs, the lack of marketing, the inability to record, and limited playing time per disc (some movies had to have 4 sides to contain the whole movie and you had to turn the disc over to continue watching the movie).

Most prohibitive was the price. At its height, a typical movie-only disc would cost approximately $35, with some of the deluxe box sets reaching upwards of $125. LaserDisc players were also expensive at average prices of around $1,000.00, but in the 1980's, laserdisc was "the" way for consumers to watch movies in "high-resolution".

Today you can buy a movie on LD for about $3.98 in second-hand stores and LD players are available from individuals for $50.

To justify the high price, laserdisc manufacturers pioneered many of the features that DVD consumers now take for granted: digital audio (along with Dolby Digital and DTS), THX mastering, secondary audio channels, commentary by the filmmakers, and supplemental material about the movie in question. The best box sets were archives of information detailing every aspect of the film's production.

Laserdisc, LD, or video laser disc was the first optical disc storage media, and an industry-wide term for consumer laser video. During its life, the format has also been known as LV (for LaserVision, actually a player brand by Philips). The players are also sometimes referred to as VDPs (Video Disc Players). Before release it was promoted under the name "Discovision".

LaserDisc was invented by David Paul Gregg in 1958, patented in 1961 and 1969, and first demonstrated by Philips and MCA (Music Corporation of America) in 1972. It was available on the market in 1978, or about the same time as the VCR and six years earlier than the CD. There are more than 1 million players in home use in the U.S. (compared to 85 million VCRs), and more than 4 million in Japan (ten percent of households). LaserDisc has now been largely replaced by DVD.

ABOUT LASERDISC:

Video was stored on LD as an analog signal, while audio could be stored in a combination of several different formats. Like on a CD, the surface of the disc is an aluminum foil covered by pits and lands, but whereas on a audio CD (or DVD) the pits and lands will signify binary codes, on a LD the distance between two pits represents an analog sample level, the accuracy of which is dependent on the quality of the measurement.

NTSC LDs carried two analog audio tracks, plus two uncompressed CD-quality PCM digital audio tracks. PAL discs could carry one pair, either analog or digital. Some later LDs featured 5.1 channel Dolby Digital in place of the right analog audio track, and a small number included 5.1 channel DTS in place of the standard digital tracks.

Laserdiscs were recorded in one of two formats: CAV (constant angular velocity) or CLV (constant linear velocity). CAV discs were spun at a constant rotational speed during playback, with one video frame read per revolution, whereas CLV discs spun progressively slower as the disc was played from inside edge to outside edge. CAV could hold up to 30 minutes of content per side, while CLV could hold twice that. The advantage of the CAV format was that its simpler playback method allowed "trick play" features such as freeze frame, slow motion, and reverse on all LD players, unlike CLV which only supported those features on high-end models with digital video buffers. The vast majority of titles were only available in CLV.

LD had a number of advantages over VHS. It featured a far sharper picture and level of sound quality, with the ability to deliver multiple audio channels, both analog and digital. This allowed "special editions" of movies with extras like director commentaries to be released. Access was random, meaning that one could go to any point on the disc very quickly (depending on the player and the disc, within a few seconds at the most). As LDs were read optically instead of magnetically, a properly-manufactured LD would theoretically last beyond one's lifetime, and as the discs had no moving parts, they were cheaper to manufacture.

The format was not without its disadvantages. The discs were 30 cm (12 inch) across, and were both fragile and heavy. There was no way for a home user to record to an LD. Depending on the format, each side of an LD could hold at most 30 or 60 minutes of content, and then the disc would have to be turned over. Most players did this automatically by rotating the optical pickup to the other side of the disc, but except in high-end models with a pre-read buffer, this was accompanied by a pause in the movie of around 10 seconds, and if the movie was longer than two hours, it eventually required putting in a second disc.

Many early laserdiscs were not manufactured properly. Sometimes a substandard adhesive was used to sandwich together the two sides of the disc, causing the disc to delaminate slightly and allowing oxygen to cause the metallic part of the discs to oxidize. This eventually destroyed the disc, a process known as "laser-rot" among LD enthusiasts. (Early CDs suffered similar problems, including a notorious batch of defective discs manufactured by Philips-DuPont Optical in Europe during the early 1990s.)

The format was not well-accepted outside of videophile circles in North America, but became more popular in Japan. Part of the reason was marketing. In North America the cost of the players and discs were kept far higher than VHS to make up for lack of demand. In Japan, LD was marketed like DVD (LD's replacement) was on its release—prices were kept low to ensure adoption, so in Japan an LD and a VHS tape were often identically priced. LD quickly became the dominant format-of-choice amongst Japanese collectors of anime, helping drive its acceptance.

A very small number of LDs were mastered, exclusively in Japan, using an anamorphic image technology, similar to the 16x9 anamorphic system used in DVDs. Among the very few films available in this format were Terminator 2, Basic Instinct and Luc Besson's Atlantis. Displaying the squeezed image correctly required a widescreen television set, which at the time cost considerably more than a standard set, and as a result the format never caught on.

The compact disc for audio was based on the laser disc technology. One reason for the (mostly) failure of laser discs may have been that it was not possible to record them, and the competing video cassette recorder devices could record using tape cassettes.

Although LDs and their players have been completely supplanted by DVD, many LDs were considered definitive releases of movies and are still highly coveted by movie enthusiasts. Boxed multi-disc LD editions of several films are prized as collector's items.

The laserdisc was the precursor to the DVD, offering superior video and sound capabilities compared to any available consumer video format prior to DVD.

Laserdiscs can display 425 horizontal lines of video information, nearly double that available from VHS tape. Laserdiscs also contain CD-quality digital sound and many now include Dolby Digital or DTS soundtracks as well.

Laserdiscs contain two digital audio tracks and two analog audio tracks. The analog tracks are commonly used for commentary by the director or, in recent years, for Dolby Digital encoded surround sound (the Dolby Digital information actually uses only one channel leaving one channel open for commentary or a mono soundtrack). The digital audio tracks carry audio signals in the same way as compact discs. However, DTS laserdiscs use the two digital audio tracks to store DTS digital surround sound information.

The video signal on a laserdisc is not recorded digitally but is an analog, composite video signal translated into digital language (binary) and then decoded back into an analog format for display. The video quality of laserdiscs exceeds that of every consumer format besides DVD. DVD offers 540 horizontal lines of resolution with an overall better picture quality due to its pure digital format (the output of DVD is rarely a complete 540 lines and often falls to 480 lines or so).

Laserdiscs are double sided holding information on both sides of the disc (like many DVDs but unlike traditional compact discs). Also, laserdiscs are available in two formats - CAV and CLV. CLV discs hold about one hour of video on a single side of the disc while CAV discs hold about 30 minutes of video on a single side. CAV discs offer a very slight improvement in video quality. Their primary advantage is their ability to offer special effects such as slow motion, freeze frame, and frame-by-frame advance. These special effects features are not available on CLV discs without a special memory feature on the laserdisc player.

Laserdiscs come in two prominent flavors: A CLV-format disc can contain up to one hour of material per side, and a CAV-format disc will hold up to 30 minutes per side. The advantage to CAV is that it will have a slightly sharper picture, will have slightly more stable colors, and allows access to freeze-frame and slow-motion functions. For the most part, visible difference between the two is slight and a mid-level laserdisc player with digital field memory can simulate the freeze-frame and slow-motion functions on CLV, but with reduced resolution in these modes.

Any laserdisc player will be compatible with both CLV and CAV, and many disc titles contain a mixture of both formats, sometimes CLV on one side of a platter and CAV on the other. In addition, many players have auto-turn mechanisms built in to make side changes less obtrusive. The typical auto-flip side change lasts about 7 seconds. Depending on the player, the screen may appear entirely black or may freeze on a still from the movie during the pause. Any movie with a running time over 2 hours will require a second platter, and this means getting up to change the disc.

When DVD hit the market in the late 1990's, it was given a huge marketing push that has been very successful in educating consumers on the benefits of high-resolution video. DVD is essentially a refinement of laserdisc technology. The disc size is smaller, resolution is modestly increased about 15%, side breaks are for the most part eliminated, and most importantly the price is lower. At this point, most DVDs cost approximately $7.50 - $24.99. It has been very popular as a result.

The Video

Even though a laserdisc may look like an oversized CD (or DVD), the picture signal it carries is actually analog in format. Only the PCM audio tracks are digital.

In direct comparison on a typical television monitor, the difference in picture quality between laserdisc and DVD is noticeable but slight. DVD is a little sharper and can achieve deeper colors without introducing signal noise as some poorly-mastered laserdiscs will. A well-mastered laserdisc, however, will hold up very well and, depending on the respective mastering quality, may even look better than a comparable DVD edition of the same film. For those with more expensive video display equipment, both formats allow S-Video connection for better color clarity. DVD goes a couple of steps further by also offering the advanced component-video connection as well as 16:9 anamorphic enhancement for increased resolution on widescreen monitors, which are advantages in its favor.

The Sound

The audio is a different story. Listening in 2-channel stereo, laserdisc audio almost always sounds richer and fuller than its compressed DVD counterpart. DVD sound quality is generally acceptable, but barring substantial mastering differences the 2-channel downmix sounds thinner and less vibrant than the uncompressed PCM audio on a laserdisc. Both formats offer Dolby Digital and DTS 5.1 channel surround sound for those with high end audio equipment, and these soundtracks tend to be closer in quality.

Laserdiscs have four separate and distinct audio channels. Two carry the PCM digital stereo signal and two carry the analog stereo. If a laserdisc includes a Dolby Digital 5.1 track, that signal is distributed in RF-modulated form through one of the analog channels. The other analog channel usually has either a mono sound mix or an audio commentary. This leaves both digital stereo tracks free.

The advantage to this method is that the 5.1 mix and the stereo or Dolby Surround mix are kept forever separate.

DVD has the potential for even more audio tracks, but the disc producers almost never use them for this purpose. They usually fill them with extra commentaries or foreign-language soundtracks, if anything. DVD also has one feature that sounds in theory like a great innovation but winds up being its greatest curse. All of the audio on a DVD is Dolby Digital-encoded. The player then is capable of taking the 5.1 mix and (within the player itself) down-converting this into a regular 2-channel stereo or surround mix for those people who don't have 5.1 surround sound.

Why this is such a problem? In preparing the audio for this down-conversion process, many compromises have to be made. One of two things usually happens:

1) The disc producers will favor the 5.1 track at the expense of the stereo downmix. One common mistake is to direct all of the bass in a soundtrack towards the LFE channel, leaving none whatsoever for the stereo mix. If you listen to it in stereo or Pro-Logic, therefore, important parts of the sound design may be practically silent. Or,

2) The disc producers will compromise the 5.1 track in order to accommodate more favorable down-conversion. If listening in Dolby Digital the bass is not going to be as deep as it should be, and the discrete sound effects will be limited.

This second process is the more common and leaves both soundtracks at a disadvantage. A simple fix to this would be if all disc producers would simply include separately both a 5.1 mix and a 2.0 mix on the same disc. A few do this, but very few and it is becoming rarer all the time. Even when they do, the 2.0 mix is not going to sound as good as the uncompressed PCM digital on laserdisc, but it will at least be closer and the 5.1 should be the same on both.

Given this, one might think that DTS audio, which remains separated from the PCM or Dolby Digital mix on a disc, would remain uncompromised. Sadly, this is not the case. DTS requires significantly more disc storage memory than Dolby Digital. In order to keep everything on a 5" platter, this means that either the bitrate allotted to the picture quality must be reduced to make room, or the DTS signal must be processed at a lower bitrate. Again, these compromises are not necessary on the laserdisc format.

The Legacy

The introduction of DVD has effectively destroyed the market for laserdiscs in the United States. In the years before DVD, laserdisc was the definitive collector's medium for high resolution video, producing a tremendous volume of output (estimates say approximately 15,000 titles) and some of the finest archive editions of classic movies, many of which may never be reproduced on DVD due to rights issues.

During its prime, there was something very special about being a laserdisc collector.

Unlike the region-blocked DVD players, any laserdisc player purchased in the United States will be compatible with NTSC discs imported from Japan or Hong Kong.