Subject: The Laserdisc FAQ - part 1/4
Date: 5 Mar 1996 16:20:44 GMT
NNTP-Posting-User: leopold


                            LD THE LASERDISC FAQ LD
                                       
                         I) INTRODUCTION TO LASERDISC
                                       
   This page is "http://www.cs.tut.fi/~leopold/Ld/FAQ/Introduction.html".
   
   
   This page is maintained by Henrik 'Leopold' Herranen
   
   The whole FAQ file is available at
   "http://www.cs.tut.fi/~leopold/Ld/FAQ/index.html".
   
   <-- Index Hardware -->
     _________________________________________________________________
   
   
   
1. Intro to LD Technology

   
   
  1.1 WHAT IS LD?
  
   From Bob Niland's (rjn@csn.org) LD#01: ..but it can't even record?
   
   LD stands for LaserDisc, the industry-wide term for consumer laser
   video. During its life, the format has also been known as LV
   (LaserVision) and CDV (Compact Disc Video). The players are also
   sometimes referred to as VDPs (Video Disc Players) and Sony calls them
   MDPs.
   
   LD was first demonstrated by Philips and MCA in 1972, and has been on
   the market since 1978, or about as long as VCR and six years longer
   than 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 (10
   percent of households there). The U.S. installed base is increasing at
   more than 15,000 units per month. 
   
  1.2 WHAT ARE THE ADVANTAGES/DISADVANTAGES OF THE LASERDISC FORMAT?
  
   In real short, a bright and detailed (as opposed to murky and grainy
   VHS) picture, sound that sounds like a CD on new movies and clearer
   than you ever thought it could be on old ones, and the ability to blow
   your friends away with a snazzy picture and booming sound that make
   VHS look like, in James Cameron's phrase, "crap-vision."
   
   LD advantages
     * Picture quality. Laserdiscs are by far the best-looking home video
       system available. And although NTSC is a inferior TV system
       compared to PAL, PAL broadcasts almost never look as good as the
       better NTSC LDs. There is more resolution, and less noise and
       time-base errors compared to other analog home video systems.
     * Audio quality. The quality of stereo digital sound on LDs is
       exactly as on CDs and 5.1 channel AC-3 can go far beyond any
       2-channel audio reproduction format.
     * Letterboxed editions. It is fairly easy to get your favourite
       movie in the theatrical aspect ratio on LDs. This was my final
       reason to buy a LD player.
     * Special editions. Because of the extraordinary capabilities of LDs
       (multiple audio channels, still-frame archives), there are special
       editions of films that gives you real in-depth information about
       your favourite movies.
     * Random access.
     * Full still-frame capability on CAV discs, and still-field with
       some players on CLV discs.
     * Durability. LDs are read optically. They will last forever if you
       treat them well.
     * Cover art. The covers look much nicer than VHS covers because they
       are bigger.
     * The discs look beautiful, shining in all the colours of the
       rainbow.
     * With few high-end exceptions, LD players can also play CDs.
     * Status. All you friends will envy you when you have such a nice
       player.
       
   LD disadvantages
     * You cannot record. Laserdiscs are a strict playback only media.
     * The sideflipping blues. As a CLV disc can only hold up to 60
       minutes per side (72 in PAL) and a CAV disc can only have 30
       minutes (36 in PAL), you have to turn the disc at least once for
       every movie if you don't have a double-sided player.
     * Price. Compared to VHS, LDs are more expensive to manufacture and
       a movie on LD does usually cost more than on VHS. The reason to
       this is partly because of the media and partly because the masters
       are usually given a much better treatment. Without good masters
       LDs would look just as crappy as VHS.
     * Availability. Especially here in Finland laserdiscs are hard to
       find. In practise they have to be ordered from the USA, which is
       always little more troublesome than going to the nearest
       supermarket. Fortunately these days several LD retailers have
       Internet access and www pages.
     * No subtitles. If you are not lucky enough to understand English
       fluently, you won't get much out of LDs. There are no laserdiscs
       with, say, Finnish subtitles. It is technically easy to have
       different language subtitles on PAL LDs as teletext pages, but
       unfortunately the smaller language groups are never included.
     * Fewer rental outlets.
     * Title availability lower and more unpredictable than VHS.
     * Laser rot. In some pressings there are discs that detoriate as
       time goes by. This may be caused by bad glue when gluing the two
       disc sides together or air bubbles being left inside the disc,
       which will cause the aluminium layer to oxidize.
     * All the best pressings are NTSC. This means that in a PAL country
       you need an NTSC capable TV set to see the movies correctly and
       you can't record the discs on tapes.
     * The picture on the discs are in the composite domain. This is the
       same as with broadcast television, but nevertheless it makes it
       hard for a television to decide which parts of the picture are
       luminance (black and white) and which parts are chrominance
       (colour) information.
     * The players may have high mechanical noise.
     * The discs are big.
       
   
     _________________________________________________________________
   
   
   
2. Advantages

   
   
  2.1 IS IT TRUE LASERDISCS WILL OUTLIVE ME?
  
   From Bob Niland's (rjn@csn.org) LD#01: ..but it can't even record?
   
   As with CD, and unlike tape formats, LD is a non-contact medium during
   play. There should be no wear in normal use, even if you freeze a
   single frame on screen for hours.
   
   The theoretical shelf life of an LD that is "properly manufactured"
   and properly stored is the same as for CD -- essentially unknown, and
   possibly longer than the photographic negatives/prints from which the
   disc was made. There are no known deterioration modes for properly
   made and stored discs.
   
   Contrast this with an optimistic shelf-life of 20 years for magnetic
   tapes of all kinds (less if used often). Tapes have several known
   deterioration modes: print-thru, binder breakdown, base stretch, and
   physical abrasion wear and signal loss due to external fields
   (magnetized VCR components, speaker magnets, CRT deflection coils,
   etc.)
   
   Note the emphasis on "properly made disc" above. I have separate
   articles available on LD quality (LD#04), identifying LD defects
   (LD#17) and the interpretation of LD mint marks (i.e. who cast or
   pressed it, LD#09).
   
   Discs do fail on the shelf, and experience other manufacturing defects
   more immediately evident. I have had several discs with "laser rot". I
   have also purchased discs with contaminants under the acrylic.
   
   The initial defect rate for LDs is lower than for pre-recorded VCR
   tapes. The rate seems to be slightly higher for LDs (about 2%) than
   for CDs (which are about 1%). 
   
  2.2 IS THE PICTURE REALLY BETTER THAN MY VCR?
  
   Pioneer pitches LD as "60% sharper" than VHS. LD image quality is
   roughly comparable to standard 16mm film, VHS is roughly comparable to
   8mm film. There are no home video formats comparable to 35mm or 70mm
   film.
   
   The pulse-FM data structure on an LD (unlike ordinary VHS/Beta), is
   defined to hold all the information present in the composite video
   signal. Depending on source material and the transfer to disc, LD is
   above live TV broadcast quality: For NTSC, this is 425 TVL (luminance
   lines horizontally) and about 482 scan lines, compared to 330x482 for
   broadcast. For PAL, the numbers are 450x560 and 400x560, respectively.
   
   
   Compare this to 250x482 for typical VHS (recorded, pre-recorded is
   probably less). Only recently have Super-VHS and ED-Beta approached LD
   capability. Of course, pre-recorded material is not widely available
   in these VCR formats. Even using S-VHS/ED-Beta to tape off-air still
   only reaches the 330x482 of the broadcast signal (400x560 in PAL
   countries).
   
   Compared to LD, all consumer tape formats also fall short in time-base
   stability, chroma resolution, video noise and audio fidelity.
   
   Although the video signal-to-noise ratio (s/n) appears to be about the
   same for LD and VCR hardware, it is probably not the same for
   mass-produced pre-recorded material. The LD process (casting or
   stamping) does not degrade the signal from master to copy. The tape
   process, magnetic contact printing, does.
   
   All LD players have time-base-correction; mechanical, optical, analog
   electronic or digital. TBC eliminates the horizontal line jitter and
   color errors common on tape. 
   
  2.3 WHAT ABOUT THE SOUND QUALITY?
  
   Laserdiscs can currently have three different kind of sound. These
   different sound schemes are gone though in this chapter.
   
   All sound combinations are not possible. The possible combinations
   are:
   
   NTSC discs:
     * 2 analog channels (last discs like this were made in the 80's)
     * 2 analog channels + 2 uncompressed digital channels
     * 1 analog channel + 2 uncompressed digital channels + 5.1 AC-3
       channels
       
   PAL discs:
     * 2 analog channels (last discs like this were made in the 80's)
     * 2 uncompressed digital channels
       
   
   
    2.3.1 Analog channels
    
   This is the old way. Originally LDs had only 2 analog audio channels,
   that were considered of high quality those days. However, especially
   the right audio channel has problems with loud high voices, and it may
   break in total distortion.
   
   Most newer discs have a noise reduction called CX on the analog audio
   channels. CX noise reduction can be turned on and off anytime on a
   disc by the player (controlled by the disc itself). On AC-3 discs, or
   on discs that have separate contents for the left and right analog
   channel, CX can't be used (without problems).
   
   The audio might be considered subjectively little worse than VHS
   Hi-Fi.
   
   On NTSC discs, analog audio channels are nowadays often used to carry
   extra information, like commentary soundtracks. This can't be done
   with PAL discs, where analog and uncompressed digital channels are
   mutually exclusive. With NTSC discs, the right analog sound channel
   can be sacrificed to give the consumer AC-3.
   
   The last players with analog-only sound were made in 1989. 
   
    2.3.2 Uncompressed digital channels, or PCM channels
    
   The 2 uncompressed PCM-encoded digital channels follow the same high
   specs as CDs: a sample rate of 44.1 kHz (actually 44056 Hz for NTSC)
   and 16 bits / channel keeps the sound as good as it can be given there
   are only two separate channels. Thus, the sound quality easily
   surpasses that of any home VCR of today.
   
   The uncompressed digital channels are the main audio reproduction
   system of today. Along with a Dolby Surround Pro-Logic decoder you may
   get a 4-channel output with 3 channels (front left, front center,
   front right) of full bandwidth (5-20,000 Hz) and 1 channel (back) with
   limited bandwidth (100-7000 Hz). Although only a limited amount of
   panning is allowed and some effects can't be done at all, the beauty
   in Pro-Logic lies into its ability to encode 4-channel sound on any
   stereo media.
   
   PAL LDs can only have either analog or uncompressed digital audio.
   
   Uncompressed digital audio has been used for 10 years now, and all new
   LDs have been with digital sound for years now. The last NTSC LDs
   without digital sound were done in the late 80's. 
   
    2.3.3 AC-3, or compressed digital channels
    
   This is a new sound system, and LDs utilizing Dolby AC-3 have been
   manufactured since the beginning of 1995. At this point there are only
   few players with AC-3 capability, and some external AC-3 decoders that
   you need to play AC-3 discs. However, adding an AC-3 RF output to
   absolutely any LD player is trivial (See the Hardware section), and as
   AC-3 will be the sound system for both American HDTV and DVD, more
   receivers are very soon to be reality.
   
   AC-3 replaces the right analog audio channel of NTSC LDs with a 384
   kbit/s data stream that can be decoded to 5+1 channels of sound. This
   system is sometimes called a 5.1 channel sound system, which means
   that 5 channels (front left, front center, front right, back right,
   back left) are of full bandwidth (5-20,000 Hz), while the 6th channel
   is a special subwoofer channel (2-120 Hz) that will be used only when
   the movie maker want to have heavy bass.
   
   The AC-3 track is heavily compressed: while an uncompressed digital
   channel use some 700 kbits/s, an AC-3 full bandwidth channel can only
   use some 75 kbits/s (average). However, because perceptual coding is
   used and most of the time almost all of the sound energy is
   transmitted to the center channel, the actual compression ratio is
   most of the time nearer 3:1 than the presented 10:1 ratio. During my
   early tests (Crimson Tide, Star Trek Generations, Die Hard), I have
   been able less than 10 times to hear any artifacts that could be
   compression artifacts.
   
   AC-3 is only available on NTSC discs. PAL discs can only have either
   analog or uncompressed digital audio channels. Thus, using the right
   analog audio channel for AC-3 would mutually exclude uncompressed
   digital audio channels, and all current owners of PAL LD players would
   totally lose the benefit of digital sound. As the PAL LD market is
   already much smaller than the NTSC market, incompatibility of this
   magnitude would probably kill it, especially when all players can't
   even play PAL analog audio!
   
   AC-3 is totally different from anything previously available at the
   home video market. It is a major breakthrough in home theatre audio
   reproduction, and to my opinion the jump from plain stereo to Dolby
   Surround Pro-Logic is smaller than the jump from Pro-Logic to AC-3. 
   
  2.4 WHAT COOL FEATURES CAN I EXPECT OUT OF LASERDISC PLAYERS?
  
   From Timm Doolen
   
   Speaking strictly of the capabilities of the hardware, and not the
   wonderful things labels are doing with software these days (which will
   be discussed in more detail in the software section):
   
   Unlike tape formats, laserdisc is not a linear format. Like CD, you
   can go to the exact position on the disc you want. On CLV, you can
   position the disc to the nearest second. On CAV, you can seek to the
   frame number.
   
   Most discs also have chapter marks, similar to tracks on a CD. Seeking
   frames/chapters is extremely quick on CAV discs because the speed of
   the disc does not have to change. Seeking time/chapters on CLV discs
   depends on the distance between the starting and end points, but never
   takes more than four to six seconds. Definitely faster than any rewind
   or fast forward on a VCR.
   
   All players and discs can pause and search forward and back. Unlike
   VCR, there is no media or player wear when this is done.
   
   CAV discs can also play forward and backward at variable speeds, from
   1/90 normal speed to 10 times normal speed. Single-frame-step forward
   and backward is also available. Some newer players have a "jog wheel"
   that allows variable speed slow/fast motion. On most good pressings,
   the still-frame has the same resolution as the moving image, unlike
   VCR which often has blurring. A CAV LD can store 54,000 individual
   still images per side. The more expensive players can also
   freeze-field on CLV discs. 
   
  2.5 CAN I PLAY CDS ON A LASERDISC PLAYER?
  
   From Timm Doolen
   
   Yes. All current all LD players except a few high-end units can play
   5-inch audio CDs. They are not usually as high quality as comparably
   priced CD players and often do not have as many high-end features, but
   they are not bad CD players. Some players have separate drives to spin
   audio-only CDs.
     _________________________________________________________________
   
   
   
3. Disadvantages

   
   
  3.1 CAN I RECORD ONTO A LASERDISC?
  
   Excerpted from Bob Niland's (rjn@csn.org) LD#01 Revised: 04 Jul 94
   
   No. Nor with CDs and LPs. Even if an economical recording LD machine
   is ever introduced, it is too late for LDs to dominate the video
   market the way that VCRs have. In audio, if you want quality playback,
   you get a CD or LP player. If you want to record, get a cassette or
   DAT deck.
   
   The typical LD owner is likely to have both a VCR and an LD. Lack of
   recording is really a non-issue as the LD product is currently
   positioned. 
   
  3.2 DO LD PLAYERS COST MORE THAN MY VCR?
  
   Excerpted from Bob Niland's (rjn@csn.org) LD#01: Revised: 04 Jul 94
   
   New LD players run from $300 (discounted) to $3,500. You can get a VCR
   for under $200. If you are concerned about features, the prices of
   comparable LDs and VCRs are about the same.
   
   You can get a used player from $100 up. The only significant missing
   feature on pre-1987 players is digital sound. The video performance
   appears to equal Pioneer's current low-end machine (CLD-S201).
   Conventional wisdom in the LD world says to avoid players prior to the
   VP-1000 (circa 1981).
   
   Having once bought a used VCR, I would not do that again (worn out
   head). An LD player seems less prone to wear, and even if it doesn't
   work properly, at least it won't eat your media (as long as you
   remember to remove that pesky shipping screw :-). 
   
  3.3 CAN I RENT LASERDISCS?
  
   Excerpted from Bob Niland's (rjn@csn.org) LD#01: Revised: 04 Jul 94
   
   Unless you live in a major market (and in North America), you may have
   trouble finding a rental outlet. There are reportedly some 5,000 LD
   stores in the U.S., including a few chains, and over a dozen national
   mail-order sources.
   
   If you are renting for auditioning of the program material, rather
   than for routine viewing, this is not a big deal. Rent tapes and buy
   discs. Or simply borrow discs. 
   
  3.4 I'VE NEVER SEEN A COPY OF MY FAVORITE MOVIE ON LASERDISC BUT IT'S BEEN
  OUT ON VHS TAPE FOR YEARS. WHY?
  
   From Timm Doolen
   
   Although the list of titles available on LD grows every day, several
   popular titles have never been in print or were available years ago,
   but are no longer in print (e.g. several of the Disney animated
   movies, which are usually not available on VHS either). The lack of
   software is usually cited by laserdisc opponents as one of the reasons
   to not get into LD. But the list of titles is very rich, and with more
   consumers and consumer pressure, more titles will be released on LD.
   What's amazing is how many titles there are to choose from considering
   the limited number of consumers. Personally, unless I win the lottery,
   I'll never be able to purchase all the titles I want to own, because
   the labels are producing them faster than I can buy them. So I usually
   don't worry about hard-to-find titles, because I know sooner or later
   the labels will release it if they can make some money off of it. In
   the meantime, my want list of released titles constantly outgrows my
   ability to purchase those titles. However, there is some sort of
   cosmic law (you might call it a corollary to Murphy's Law) that no
   matter when you start collecting LDs, at least one of your top five
   favorite movies will either be out-of-print or never released.
   
   There's also imports....
   
   In some cases, if a title is not available in domestic release, you
   may be able to find it as an import. Japanese LDs may have modified
   contents. Japanese moviegoers are more critical than Americans, and
   insist on original-language presentation, rather than dubbing. So
   unless the disc is widescreen, the Kanji subtitles may appear
   on-screen and in-picture.
   
   An accurate Japanese LD catalog is required to know for sure. Refer to
   LD#02 for more information on imported LDs.
   
   Also, Japanese films censor some types of nudity acceptable in U.S.
   [R] rated films. "THX-1138", George Lucas' first film, available on
   disc only in Japan until 1992, has flesh-colored airbushing. There are
   no uncensored [X] or [NC-17] American films at all in Japan. However,
   there's a huge market over there for X-rated anime. 
   
  3.5 HOW COME WHEN I WATCH A LASERDISC, I HAVE TO FLIP THE DISC OVER?
  
   From: Timm Doolen
   
   CLV discs can store 60 minutes per side (72 for PAL discs), CAV allows
   30 minutes per side, requiring a side change at the end of each side.
   This is more of annoyance to some than others, and is a definite
   reminder that you are not watching a movie in the theater. The CAV
   version of Ben Hur requires 7 disc changes. Disc changes take at least
   several seconds, because the disc has to come to a complete stop and
   then start spinning again (whether you flip it by hand or have a
   multi-side player), each process taking at least two to three seconds.
   
   
   In recent years, two-side players have become more and more
   affordable, allowing you to watch up to two hours uniterrupted on CLV
   discs, which covers a large percentage of movies.
     _________________________________________________________________
   
   
   
4 Other differences between laserdisc and VHS

   
   
  4.1 WHAT ARE THOSE BLACK BARS AT THE TOP AND BOTTOM OF MY SCREEN?
  
   From Timm Doolen & Michael Gebert (MGMax1919@aol.com)
   
   For a detailed look at aspect ratios, look in section 12 of this FAQ.
   What follows is a nutshell explanation of letterboxing and aspect
   ratios.
   
   The original aspect ratio of films from the beginning of the century
   to the early 1950s was 4:3 or 1.33:1. When television came along in
   the '40s it modeled its ratio after this number. When television
   started becoming popular, the film industry responded by introducing
   wider and wider pictures to the audience through various means,
   including wider film gauges such as 70MM, multiple projectors (as with
   Cinerama), and most commonly today, anamorphic projection, which uses
   special lenses to squeeze a wider image onto 35MM film. Aspect ratios
   for movies in the 50's and early 60's ranged from 1.33:1 all the way
   out to 2.8:1 for Cinerama.
   
   By the mid to late '60s, most of the thunder of widescreen was over
   and many in the industry went back to shooting movies on flat 35mm
   film (non-anamorphic) and matting the upper and lower portions of the
   image to give about a 1.85:1 image.
   
   When these films were transferred to another format to be shown on TV,
   you had to do one of three things: lose part of the image to cropping,
   letterbox the image so it would fit inside the tube or squeeze the
   image horizontally by not using the anamorphic lens during playback.
   
   Of course in the '50s and '60s they didn't have 27", 35" and 50" TV
   screens, so letterboxing was not an option. Neither was cropping,
   because a 2.35:1 image is almost twice as wide as a 1.33:1 and much
   important action would be lost if you just cropped the sides off a
   2.35:1 image. So they either squeezed the image, which causes the
   actors and objects to look very thin, or they gave it a pan & scan
   (P&S) transfer -- or both, in some extreme cases (often title credits
   will be squeezed, while the movie will be P&S'd).
   
   For P&S, a telecine operator watches the movie as it is being
   transferred, and follows the important part of the frame by panning,
   thus the term pan and scan. Some P&S transfers of widescreen movies
   are OK, others are horrible. Occasionally if two characters are on
   opposite sides of the frame, you either see one or the other, or both
   of their noses in a P&S transfer.
   
   Of course problems with P&S are: it throws the image composition off,
   it still excludes important information in most scenes (such as entire
   characters that are important to the shot), and it produces motion
   artifacts if people are moving in the frame during a pan. And not
   least of all, it adds a whole style of "camera" movement on top of
   whatever the director had already done (or not done), sometimes
   significantly altering the feel of a film.
   
   So in the 1980s when laserdisc started becoming a popular format,
   consumers started demanding films be shown in their original aspect
   ratio of 2.35:1, 1.85:1 or whatever. The Voyager/Criterion company was
   instrumental in starting the letterbox trend - introducing
   letterboxing with their release of Lawrence of Arabia, and
   letterboxing all subsequently released movies that had non-Academy
   aspect ratios. (Woody Allen also insisted on a letterboxed
   presentation of his film Manhattan on cable and VHS around the same
   time.)
   
   A laserdisc letterbox movie should always look better than a VHS
   letterbox movie because it has more lines of resolution to devote to
   the image. But there is nothing about the medium itself that prevents
   VHS movies from being letterboxed (in Europe, letterboxed PAL releases
   are very common). But the average consumer who owns a VCR and a 19" TV
   usually wants the full screen filled. To many consumers the "black
   bars" at the top and bottom of the image, which are a natural result
   of letterboxing, detract from their movie-viewing pleasure.
   
   To the movie lover and video enthusiast, it is a choice they will have
   to make for themselves. But to be objective, it is best to view movies
   of several different aspect ratios in both letterbox and pan-and-scan
   format.
   
   Some popular LBX movies on LD and their aspect ratios:
     * The Searchers 1.66:1 (VistaVision)
     * The Alamo 2.2:1 (Todd-AO)
     * Star Wars 2.35:1 (Panavision)
     * Lawrence of Arabia 2.35:1 (Super Panavision 70)
     * 2001: A Space Odyssey 2.20:1 (Super Panavision 70)
     * The Good, the Bad and the Ugly 2.35:1 (Techniscope)
     * It's a Mad Mad Mad Mad World 2.75:1 (Ultra Panavision 70)
     * Ben-Hur 2.76:1 (MGM Camera 65)
     * How the West Was Won 2.8:1 (Cinerama)
       
   
   
  4.2 WHY DO LASERDISCS COST SO MUCH?
  
   From Bob Niland's (rjn@csn.org) LD#01: ..but it can't even record?
   
   Discs cost about twice as much to manufacture as tapes, but new
   release discs often sell for less than new release tapes.
   
   VHS tapes are the dominant home video medium. Most people rent tapes
   rather than buy them. The film studios don't get a percentage of the
   rental revenue, just the income from the initial sale of each
   prerecorded tape. Video stores are in hot competition to get new
   titles fast, so it is somewhat a "captive market." The first tape
   sales are therefore targetted at, and priced for, video rental stores
   - not for collectors.
   
   Consequently, new tape releases are priced very high ($80-$90 is
   common). It is not until the the video store demand is satisfied that
   studios drop prices to levels attractive to individual movie
   collectors ($30-40). When that market is satisfied, prices may drop
   further for the mass market customers, $10-20 per tape.
   
   In contrast, LD has been a "sell through" market. The major purchasers
   of new LD releases are individual movie collectors. LD rentals are not
   a big market, and there is no low-end mass-market at all. LDs, even
   major titles like "Top Gun", are typically introduced at $30-40 (for
   CLV), and stay there. Many recent titles have come in at well below
   $30. Incidentally, routine 10% discounts are common for LD. I have a
   separate article, LD#14, available on LD mail order sources.
   
   Two exceptions to the generally low prices in the LD market are
   Criterion Collection and CBS/Fox. Criterion releases run from $40-70
   (CLV) and $60-125 (CAV). They are worth it because they seek out the
   finest possible source material (archival negatives, etc.) and deliver
   the most complete product, often with generous motion, still-frame and
   multi-channel audio supplements.
   
   CBS/Fox widescreen titles are about $10 higher than Criterion, and
   generally have no supplements. CBS/Fox has been testing the waters to
   see if the market will sustain this new rental-style pricing
   philosophy. It may backfire as collectors and low-volume dealers
   decide they cannot to invest $70 on an otherwise unexceptional CLV
   title. 
   
  4.3 SOMETIMES I'LL HEAR ABOUT A LASERDISC ABOUT TO BE RELEASED AND IT'S
  FOREVER BEFORE IT HITS THE STORES. WHAT GIVES?
  
   Excerpted from Bob Niland's (rjn@csn.org) LD#01:
   
   LD producers sometimes announce titles before they have the rights
   completely nailed down. This may be carelessness, but there are other
   causes as well, such as "surprise" old contracts that turn up late,
   and contain language that failed to anticipate LD (e.g. "We hereby
   assign to OneTimeVideo the LP, cassette and video tape rights to
   'Revenge of the Valley Girls III'. All other rights are retained." So
   who has the LD rights?
   
   LD producers also often announce titles after clear rights have been
   obtained, but before acceptable mastering source elements have been
   located. MGM/UA says the entire old United Artist vault materials are
   in sad shape. Criterion often announces it will offer a title when it
   gets the rights, long before they have collected, collated, annotated
   and transfered all the CAV supplements they are so famous for.
   
   The practice of pre-announcing has the advantage that the major
   dealers often offer 15% pre-release pre-order discounts, sometimes as
   high as 25% on megatitles. The dealers get a larger discount on large
   initial stocking orders, and they can pass it on.
   
   Once rights and source material have been obtained, the LD producer
   must schedule transfer time and pressing time, further complicated if
   closed- captioning or other special-processing is used. LD jacket
   artwork and editiorial content needs to be prepared as well. There are
   a limited number of video houses who perform quality, LD-compatible
   telecine transfers; fewer yet who offer digital transfers. There are
   only eight pressing plants worldwide that are routinely available for
   NTSC LDs. If they all are flooded with "megatitles", lower volume
   titles get delayed.
   
   Pressing plant capacity also affects inventories of back-titles. New
   issues often sell-out, and are not re-pressed for six months or more.
   If you are just starting out in LD, expect some frustration in finding
   all the back titles you seek.
     _________________________________________________________________
   
   
   
5. Defining the medium

   
   
  5.1 WHAT PARTIES ARE INVOLVED IN BRINGING A MOVIE TO LASERDISC?
  
   Excerpted from Bob Niland's (rjn@csn.org) LD#09: LD Mint Marks
   
   There are at least six separate entities involved in getting visual
   works from the film/tape vault onto acrylic plastic and delivered to
   your hands:
   
   
   
    5.1.1 The studio
    
   e.g. "Universal", "Touchstone".
   
   Ignoring Public Domain for the purposes of this discussion, the studio
   holds the copyright on the work in question, and usually custody of
   the archival film or tape elements. The studio may not actually
   initiate the LD release. Until recently, with a few exceptions (MGM in
   particular), the LD release was actually championed by the
   distributor. The studio merely grants permission and provides a key to
   the vault, so to speak. 
   
    5.1.2 The label
    
   e.g. "MCA", "CBS/Fox".
   
   The label hosts the release, lists it in their catalog, and may hold
   the home video rights as well. The label may also be a studio and is
   often a generalized entertainment conglomerate. There are well over
   100 "labels" on LD in the U.S. 
   
    5.1.3 The masterer
    
   (usually a manufacturer)
   
   Converts the master videotape into a "glass master" for each side of
   the disc. Normally, glass masters never leave the manufacturer's
   control, but there have been reports of mixed mint marks, implying
   that one vendor made the masters, and another made the stampers and
   media. Glass masters are used to make one or more metal stampers that
   press or cast the actual disc media. 
   
    5.1.4 The manufacturer
    
   e.g. "3M", "Pioneer".
   
   The manufacturer presses (or casts, or injection molds) the media.
   They may also manufacture the disc labels, sleeves, jackets, and/or
   assemble the end product. With the exception of Pioneer, and some
   early 3M titles, manufacturers seldom act as "labels" or
   "distributors".
   
   There are only six significant LD manufacturers in the continental
   U.S. There are at least five off-shore manufacturers that matter here,
   and perhaps more making discs in Japan for local consumption there.
   The significant sources are, in order of probability of encountering
   them:
     * Pioneer Video Manufacring (PVM)
       aka Pioneer Video, Inc. (PVI) US
       aka Pioneer Communications of America (PCA)
     * Pioneer Video Corp. (PVC) Japan
     * DADC - Digital Audio Disc Corp. Sony-US
     * DADC Austria Sony-Europe
     * 3M US
     * Mitsubishi Japan
     * Technidisc US
     * Philips-Dupont Optical (PDO) UK, "PDO"
     * Kuraray Japan
     * CBS/Sony Japan
     * DiscoVision (DVA) US - long gone
     * WEA Manufacturing (90% of Warner catalog from mid-91 to mid-93)
       
   
   
    5.1.5 The distributor
    
   e.g. "IMAGE", "LDCA".
   
   The distributor warehouses the finished product, and ships it to
   retailers. A distributor usually publishes a catalog. A distributor
   may have exclusive access to certain titles, labels and studios. Some
   labels (e.g. Warner, MCA, Voyager and Lumivision) handle their own
   distribution (although non-exclusively). With the exception of Voyager
   Press, distributors generally don't sell directly to consumers under
   their own name.
   
   There are only 2 broad-line LD distributors that really matter in the
   U.S.;
     * Image Entertainment (IMAGE)
     * Pioneer Laser Disc Corporation of America (LDCA).
       
   
   
    5.1.6 The retailer
    
   e.g. "LaserLand", "Sight & Sound", "Laser Disc Fan Club", "Columbia
   House".
   
   The retailer sells directly to the public. Retailers may source from
   multiple distributors, so they theoretically can get you anything that
   is in print (or in a warehouse somewhere). The larger chains may
   handle their own distribution. 
   
  5.2 SO LASERDISCS ARE JUST LIKE BIG CDS WITH MOVIES ON THEM, RIGHT?
  
   Excerpted from Bob Niland's (rjn@csn.org) LD#01:
   
   There are three major types of consumer laser video media:
     * 12-inch video discs,
     * 8-inch video discs, and
     * 5-inch "CD-Video" discs (CDV5).
       
   The traditional 12- and 8-inch media are of acrylic construction, and
   are always two-sided, although sometimes only one side contains
   program material. LDs are literally two single-sided discs glued
   together, and the edge of the disc is often sticky for this reason.
   
   The 5-inch (CDV5 or just CDV) is single-sided, and can contain about
   six minutes of full-motion video/audio plus 20 minutes of audio-only.
   As with CD, CDV5 is polycarbonate on the data side, and lacquer on the
   label side. Any LD player that can handle CDV5 can also handle
   audio-only CD. CDV is all but defunct in the United States but still
   popular in Japan.
   
   At present, no LD combi players can handle the new CD-I full motion
   video and VideoCD formats. Since the basic quality and nasty artifacts
   of these highly compressed formats render them less pleasant to watch
   than VHS, they aren't likely to be of interest to anyone seeking laser
   quality home theatre.
   
   CD-I and VideoCD don't appear to be much of a threat to LD. Anyone
   interested in LD is apt to be in the market because they are weary of
   the limitations of VHS. One look at 5-inch compressed digital video
   will make it clear that CD-I and VideoCD are no alternative to LD, and
   aren't even a net improvement over VHS for home theatre purposes.
   
   Other buzzwords: LD players (whether combi or not) do NOT presently
   support CD-ROM, or CD-ROM/XA (audiofiles), DVI, CD-I (interactive
   multi-media) and VideoCD formats. Until recently, only Karaoke LD
   players supported CD+G subcode text. Pioneer has "LaserActive" players
   which support CD+G, LD-G, Sega CD-ROM games, Genesis 16-bit game
   cartridges, and a new format: "MegaLD" 8- and 12-inch LD-ROM2 discs. 
   
  5.3 WHAT'S ALL THIS TALK ABOUT NTSC, PAL AND SECAM?
  
   Currently there are three dominant video standards is the world,
   namely NTSC, PAL and SECAM. As LDs are only made for NTSC and PAL
   systems, this article will not cover SECAM. You can get more detailed
   information about the different TV systems from BBC Aberdeen,
   http://www.bbc.co.uk/aberdeen/tech.htm. 
   
    5.3.1 NTSC
    
   
   
   NTSC stands for National Television Systems Committee, and is the TV
   system used in North-America and Japan. It has 60 fields (30 frames) /
   second, 525 vertical lines of resolution (480 visible), and a 3.58 MHz
   colour carrier wave. Only LDs made for the North American and Japanese
   market are NTSC.
   
   As with VCRs, the only significant "grey market" media sources for
   North American customers are Japan and Hong Kong. Encoding is really a
   non-issue for NTSC consumers, and U.S.domestic discs are sometimes not
   even labelled "NTSC".
   
   There is a problem with movement when transferring a film to NTSC: 30
   frames/s, or 60 fiels/s of NTSC is not divisable with the 24 frames/s
   used in almost all films. The problem is solved in the following
   fashion: Two consecutive film frames lasting 1/12 s are taken. The
   first film frame is shown for 2 NTSC fields (2/60 s). The second film
   frame is shown for 3 NTSC fields (3/60 s). This makes a total of 5/60
   s for NTSC video, which also makes the 1/12 s the original film frames
   were supposed to last. This system is called pull-down.
   
   There are drawbacks in this pull-down system: to some viewers (me
   included), slow panning looks much more jerky in NTSC compared to the
   original film experience, or PAL. 
   
    5.3.2 PAL
    
   PAL stands for Phase Alternating Line, and is the TV system used in
   the civilized parts of Europe, and China. It has 50 fields (25 frames)
   / second, 625 vertical lines of resolution (585 visible), and a 4.43
   MHz colour carrier wave. PAL discs will not play on current American
   machines. The PAL LD (also called LV or CDV) catalog is about 1000
   titles at present. However, multi-standard players are available in
   Europe. These may or may not require a multi-standard TV/monitor.
   
   Because films have 24 frames/s and PAL has 25 frames/s, it is most
   convenient to show movies at the frame rate of PAL. This makes movies
   last 4% less time and makes all voices little higher. Usually this
   makes little difference, but for me watching Pink Floyd's The Wall in
   PAL is almost like torture.
   
   
   
  5.4 WHAT IS "CX NOISE REDUCTION"?
  
   From Bob Niland's (rjn@csn.org) LD#01: ..but it can't even record?
   
   CX noise reduction is the rough LD equivalent of Dolby-B for audio
   tapes. CX is only used on the LD analog channels. There has been a lot
   of debate about CX. Criterion, for example, only uses CX when the
   original audio source material has wide dynamic range (i.e. frequently
   not on early optical soundtracks mastered on film). They do not use it
   where the programs on the two channels are different, as it can cause
   decoder mistracking. 
   
  5.5 WHAT DOES CLV AND CAV MEAN?
  
   Excerpted from Bob Niland's (rjn@csn.org) LD#01:
   
   Rotation modes: LDs can be mastered for either constant linear
   velocity (CLV, variable rpm), like a CD, or constant angular velocity
   (CAV, constant rpm), like an LP. All consumer players can handle
   either format. Some releases even mix the modes, with the initial
   sides being CLV and the final side being CAV. Some films are initially
   released in both CLV and CAV "collectors" editions.
   
   CAV is also known as "standard play" or "full feature play". Only CAV
   provides all motion control capabilities on all players (at the
   expense of more platters and shorter 30 minute sides). CAV also
   provides constantly improving signal-to-noise ratio as the program
   proceeds toward the outer edge, but this is typically not that
   noticeable on properly manufactured discs.
   
   CLV is also known as "extended play". One hour per side playing time
   results in lower prices and less flipping. In return, you give up all
   the other CAV features, unless you have a high-end player with digital
   field store.
   
   The majority of disc titles are available only in CLV.
   
   A Comparison Between CLV and CAV discs on different players (NTSC
   discs):

                                               Ordinary   Digital
                                                Player    Player*
                        Capability      CAV     CLV       CLV
           Rotation velocity (rpm)      1800    1800..600 1800..600
   Maximum time per side (minutes)      30      60        60
       Simple fast forward/reverse      Yes     Yes       Yes
     Variable fast forward/reverse      Yes     No        Yes
     Variable slow forward/reverse      Yes     No        Yes
        Pause (with blank display)      Yes     Yes       Yes
Still frame (field on digital CLV)      Yes     No        Yes
                        Still step      Frame   No        Yes #
                   Seek to chapter      Yes     Yes       Yes
                      Seek to time      No @    Yes       Yes
              Seek to frame number      Yes     No        No

   
   
   * - Digital field-store CLV is a feature of the player, not the media.
   
   
   @ - Current time is stored in the vertical interval on CLV discs. That
   structure is used for frame number on CAV discs. However, the P-Q
   subcode fields, also called TOC for Table of Contents, of the digital
   audio track can contain elapsed / remaining track / side time on CAV
   discs.
   
   # - CLV still step on consumer players is either one revolution (typ
   on Pioneer), which may be several fields, or may be one frame (typ on
   Sony and Panasonic). 
   
  5.6 WHAT IS CAA THEN?
  
   CAA stands for Constant Angular Acceleration.
   
   To be exact, the discs that nowadays are entitled CLV, are actually
   CAA discs. In CAA the disc speed is not slowed down constantly, but it
   is kept constant for some time and then rapidly slowed down. The point
   in this system is to keep the horizontal sync signals aligned on
   adjacent disc tracks to keep crosstalk to a minimum. In Blaine Youngs
   (Blam1@aol.com) words:
   
   "CLV: This format is dead. The name is still used for simplicity's
   sake, but 3M is the only manufacturer which uses it. In 1982/3, there
   was a shift to CAA. This is the only format used today. (Again, except
   for 3M which incorporates a minor variant on CLV to eliminate
   crosstalk). Regardless of which format is used (CLV or CAA) it is
   still required to have crosstalk rejection code built into the
   mastering software to prevent master crosstalk. Technidisc does not
   use such software and as a result, most of their CLV stuff looks like
   crap.
   
   CAA also offers something else, 5 different encoding routines. This
   will allow for variable playback times, depending on the program. What
   happens is that the initial CAV pattern at the beginning of the disc
   is altered (lengthened or shortened as necessary) and the track pitch
   is modified. The 5 formats are CAA45, CAA55, CAA60, CAA65 and CAA70.
   CAA45 has been used only once, that I know of. Any disc side running
   less than 55:05 uses CAA55 encoding. All other discs are CAA60. There
   are 2 known occurances of CAA65 and there has never been a CAA70 disc
   released in the US."
   
   From now on, CLV and CAA discs are just called CLV for simplicity, and
   because that's what's written on the disc sleeves.
   
   
   
  5.7 WHAT IS THE QUALITATIVE DIFFERENCE BETWEEN CAV AND CLV?
  
   From Michael Gebert (MGMax1919@aol.com)
   
   While technical differences between CAV and CLV are discussed below,
   it should be noted that the choice of format is only one factor, and
   not necessarily the most important one by any means, in determining
   the eventual quality of a disc. The care taken during the mastering
   process and the condition of the source materials are of at least as
   much importance. With the improvements in mastering capabilities over
   the years, it is not unknown for a CLV disc released today to look and
   sound better than a CAV disc mastered several years ago (e.g., the new
   Criterion transfer of Citizen Kane compared with the one that was
   released in the mid-80's as the very first Criterion Collection disc).
   In short, the technical differences between CAV and CLV are
   discernable only at the ultimate point of the respective formats'
   capabilities. The best CAV disc will look and sound better than the
   best CLV disc, but a good CLV disc will look much better than an
   average CAV disc-- while even the best VHS tape won't compare with any
   competently made disc.
   
   Leopold continues with a table comparing CAV to CLV:
     * + Better colour S/N ratio. There is some minor amount of colour
       noise evident in CLV discs and in the beginning 4 minutes of CAV
       discs. After this, however, the linear speed of the disc goes high
       enough to disable any visible noise (that wasn't in the original
       masters).
     * + All special video effects available on all players. You can have
       a full resolution still-frame on all players, and you can scan
       through the disc with as perfect a picture as your TV system
       allows.
     * + The pictures can be handled as separate images. This feature is
       often used in special edition of movies to let the user see
       production fotos, manuscripts etc.
     * + The LD player can automatically pause when a CAV disc switches
       from live motion video to still frames.
     * + Faster access times.
     * + Cross-talk is generally invisible on CAV. Cross-talk usually
       appears as herringbone patterns on the screen, and can result from
       an LD mastering defect (A), player misadjustment (B), or even
       master tape problems. In cases A & B, CAV can make the problem
       invisible, because on CAV the adjacent lines are:
          + aligned in time
          + often identical to the current line
          + at least contextually related to the current line, so the
            visible effects of crosstalk are minimal or invisible
   In CLV the adjacent lines are:
          + misaligned in time even if identical in content at
            start-of-side;
          + from distant parts of the frame image (contextually
            unrelated) as the side progresses;
          + usually contain horizontal retrace interval junk (including
            large video pulses) during the active line period of the
            desired scan line, so any crosstalk is likely to be quite
            visible.
   The problems mentioned here have been mostly fixed with a technology
       called CAA, where the disc speed is changed in steps so that the
       horizontal retraces always overlap. The discs are CLV compatible,
       but the risk of getting herringbone patterns are much smaller.
     * Point defects on CAV tend to be stationary; they scroll on CLV. On
       CAV, they affect the same pixel, scan line or group of lines in a
       sequence of frames. CLV defects tend to scroll (faster toward side
       end). Which of these is more obnoxious is a matter of opinion.
     * - More disc flipping on live action video (max 30 minutes on CAV
       vs. 60 minutes on CLV (36 and 72 for PAL)).
     * - More expensive due to the higher amout of discs.
     * - More noisy, because the disc speed doesn't decrease towards the
       end of the disc.
       
   But does a CAV disk produce a better picture than a CLV disk?
   
   For free-run playback, not really. The quality difference between CAV
   and CLV is small, and much less dramatic than say, S-VHS vs VHS.
   
   Of course, for seek/still/step/slow/fast, CAV is at least twice the
   image quality of CLV, and on most players, offers functions that CLV
   discs can't duplicate. 
   
  5.8 WHAT IS THE DIFFERENCE BETWEEN DOLBY SURROUND, PRO-LOGIC, AC-3 AND THX?
  
   Excerpted from Bob Niland's (rjn@csn.org) LD#03: The soundtrack comes
   after you..., and revised by Leopold (mods to THX, added AC-3)
   
   A branded "Dolby Surround" decoder
     * sends Lt-Rt (surround) thru a delay line (typically 20 mSec),
     * then thru a 7 KHz low-pass filter (to keep natural and azimuth
       error caused left/right source phase noise from being heard as
       surround) and
     * thru a 5 db (vs 10 on audio cassette) Dolby B-type noise reduction
       circuit.
     * Lt and Rt are isolated, and may also be summed (Lt+Rt) and sent to
       the Center output.
       
       In any case, a maximum of 3 dB of separation is achieved between
       each adjacent pair of: left-center-right-surround-left.
       
   A Dolby Pro Logic decoder starts with Dolby Surround, and
     * replaces the simple Lt-Rt (surround) and Lt+Rt (center)
       extractions with an active adaptive matrix decode step. For
       signals intended for one output, this circuit attempts to cancel
       them in the others.
     * It also analyses the soundfield for signal dominance, and focuses
       the sound toward those outputs. The net result is that 30 dB of
       separation is possible between any two channels.
     * Input balance is required.
     * Lexicon Pro-Logic decoders also include an "auto-azimuth" feature
       to correct for group delay errors (time shifts) between the two
       source channels. Shifts as high as 50 microseconds are reportedly
       common in film-sourced sound (45 degree phase shift at 5 KHz).
       
   When a Dolby AC-3 -encoded laserdisc is played on an AC-3 player and
   the audio is fed to an AC-3 decoder
     * the listener is offered five discrete channels of highly
       compressed full frequency range sound (5-20000 Hz).
     * As an option, a special subwoofer channel is offered (2-120 Hz).
       
   LucasFilm THX
   
   THX is not another encoding scheme. It's just a quality assurance
   system that tries to take the most of Dobly Pro-Logic. A THX-certified
   processor starts with Dolby Pro-Logic and adds
     * Surround channel decorrelation - a digital pitch shift is used to
       make the (mono) surround signal "different" in the left and right
       surround channels.
     * Re-equalization of the front channels, to make the movie mix seem
       less "bright" in the home.
     * "Timbre Matching" - an equalization applied to the surround
       channel to make effects sound consistent when panned between front
       and surround speakers.
     * THX has also become a LaserDisc certification program. The first
       title with "THX quality" presentation parameters was the
       director's cut of "The Abyss", released in 1993. Nowadays most
       major releases has the THX certificate.
       
   THX specifies front speakers with a reduced vertical dispersion (to
   minimize ceiling reflections) and two side-mounted surround speakers
   configured for dipole radiation. THX is also a certification process
   for video programming, beginning with LaserDiscs in early 1993. As
   with Pro Logic, THX-branded audio material is not "THX encoded". THX
   mixes are merely a specific way of performing Dolby-MP sound
   mastering. A THX-certified LD presumably will have purist aspect
   ratio, source element/transfer quality, colorimetry/timing, etc. The
   telecine monitor is calibrated by LucasFilm and a "THX Vertical
   Interval Test Signal(TM)" is inserted during NTSC encoding of the
   signal.
     _________________________________________________________________
   
   
   
6. Rivals of laserdisc

   Laserdiscs are of course not the only movie media on the market. In
   this chapter I'll make a little comparison between LDs and some other
   popular video formats. For a technical comparison, look at my www-page
   Home Video Formats,
   http://www.cs.tut.fi/~leopold/Ld/VideoFormats.html. 
   
  6.1 VHS
  
   VHS is naturally the biggest rival of LDs, and in the late 80s it
   almost killed the format. Not because of the quality, but because of
   clever marketing (can you spell C-cassette, PCs and Windows-95?).
   
   Qualitywise VHS is worse in every aspect: Less luminance resolution,
   less colour resolution, more picture noise, no digital sound, tracking
   problems, plus normal tape wear and tear. But, Joe/Jane Average
   doesn't care of the picture is bad. He/she doesn't even care if 40% of
   the original area of the picture is lost in a panned and scanned (P&S)
   version of his/her favourite movie.
   
   S-VHS is much better, but there is no program material available for
   it. Enough said. 
   
  6.2 CD-I AND VIDEOCD: THE DIGITAL 5" CD-ROM -LIKE LASERDISCS
  
   Philips claims CD-I to have a clean and sharp digital picture. Sure.
   The truth just happens to be that when a film is tried to cram in the
   same bandwidth that CDs use just for sound, the result is no good.
   Although the theoretical resolution of CD-I is somewhere around
   320x256 pixels (240x256 lines), a transition from black to white can't
   happen in one pixel. This makes the real resolution look more like
   200x180 pixels. This is even worse than VHS, which has a resolution of
   somewhere near 320x585 pixels (240x585 lines) for PAL.
   
   When the images are not moving, CD-I appears to have a steady and
   non-noisy picture. But when the picture has much movement, the very
   low picture data rate of 1.1 Mbits/s makes the picture break into
   little 8x8 and 16x16 pixel MPEG-1 -compression blocks, which makes any
   action film look totally disgusting. When you are supposed to be lost
   in high action of a film, you are lost in compression blocks.
   
   One way to see, how the image is compressed, is to calculate how many
   bits are allowed for each pixel in a frame. An uncompressed 24-bit
   image uses naturally 24 b/pixel. For CD-I, the rate could be
   calculated in a following way: The total data rate is 44100x32 bits/s
   = 1.4 Mb/s. One fifth is allocated for audio, which leaves 1.13
   Mbits/s for video. Now,
   1.13 Mb/s / (320x260) pixels/frame / 24 frames/s = 0.56 b/pixel
   which leads to a compression ratio of 42:1. Now it isn't so hard to
   understand why the picture quality sucks.
   
   CD-I discs are claimed to be both NTSC and PAL compatible. This is
   carried out with an evil scheme: the discs are mastered in a way that
   makes everything appear 10% too flat on PAL TVs and 10% too tall on
   NTSC TVs. I find this way of solving problems to be totally
   unacceptable. 
   
  6.3 DVD: THE NEW DIGITAL 5" LASERDISC
  
   DVD is a new proposed 5" format, that can have digitally stored
   information comparable to several CDs. It will use MPEG-2 compression,
   and because of a high data rate it is supposed to give you a very high
   quality picture and good multi-channel audio. At this moment (winter
   1995/96) DVD is still just hype.
   
   DVD discs are also claimed to have full-frame and letterboxed versions
   on the very same discs. Future will show if this is true. I doubt it.
   
   If DVD comes, it will have some kind of component-based picture
   opposed to the composite picture in LDs, and with a RGB connection the
   colours might look a great deal better compared to LDs.
   
   Here are some specifications given for DVD by Dave Pushic
   (74775.1345@CompuServe.COM) (95-12-08):

Physical Characteristics:

Disc Diameter:                  120 mm
Disc Thickness:                 1.2 mm (2 X 0.6 mm)
Memory Capacity:                4.7 GB/single side
Track Pitch:                    0.74 m
Wavelength of laser:            650 nm / 635 nm
N.A.                            0.6
Error Correction:               RS-PC
Signal Modulation:              8-16


Specification for Audio/Video Application:

Data transfer Rate:             Variable speed data transfer, at an
                                average rate of 4.69 mb/sec for
                                image and sound.
Image Compression:              MPEG-2
Audio:                          Dolby AC-3 (5.1 channels),
                                LPCM for NTSC and MPEG Audio,
                                LPCM for PAL/SECAM,
                                (a max. of 8 audio channels and
                                32 subtitle channels)
Running Time:                   133 min. per side
                                (at ave. data rate of 4.69 Mb/s
                                for image and sound, including 3
                                audio channels and 4 sub-title channels)
File Management Structure:      Micro UDF and ISO-9660


Specifications for Computer Application:

File Management Structure:      Micro UDF and/or ISO-9660

   DVD is capable of buffering information. Thus, if there is need for a
   short burst of action, DVD can use a lower data rate and save the rest
   of the incoming data in a buffer, and then use more data for the fast
   scene.
   
   However, the average data rate of 4.69 Mbits/s containing both picture
   and sound seems quite low. This is pure speculation, but if the 3
   audio channels mentioned above are AC-3 channels, they will eat about
   1 Mbit/s, or little more. Thus about 3.5 Mbits/s is left for picture.
   Now, let's repeat the caulculation we did earlier for CD-I. First,
   we'll have to choose a resolution for DVD (no info available yet). I
   guess the resolution of DVD to be 640x560 (for PAL), which would yield
   a horizontal video resolution of 480 vertical lines, which is little
   better than PAL LD's 450 lines.
   3.5 Mb/s / (640x560) pixels/frame / 24 frames/s = 0.41 b/pixel
   A compression ratio of 59:1, which is considerably higher than the one
   for CD-I leaves me very sceptical about the picture quality of DVD.
   
   More information on DVD is available at
   http://www.unik.no/~robert/hifi/dvd/.
     _________________________________________________________________
   
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