DVD and Audio
The CD format was standardized at a time when digital recording of sound on disc was still an uncharted realm, full of possibilities and surprises, and CD technology strained at the limits of what was possible, particularly A-D and D-A conversion methods. The use of lasers to write the master discs, although not new because of the Philips “silver discs” used for video recordings, was unfamiliar to many recording companies, and the extent of the packing of bits on the CD stretched the pressing capabilities of all but a few users. Now, at least two decades on, we can see that the potential of the little CD is much greater than we could have hoped for.
DVD, originally the acronym of digital video disc, is now taken to mean digital versatile disc and refers to a more recent development of CD technology. This was originally directed to recording full-length films on CD, hence the “video” in the original title, but the idea has been extended to a universal type of disc that can be used for films, audio, or computer data interchangeably. The main difference, at present, is that there are very few DVD writing drives available, and these few are expensive by computing (although not by hi-fi) standards.
● An important feature of a modern DVD computer or TV drive unit is that it will accept conventional CDs as well as DVD discs.
The DVD holds much more data, can transfer it faster, but is as easy to reproduce by stamping processes as the older CDs (which, alas, does not mean that it will be sold at reasonable prices in the United Kingdom, even if a DVD costs so much less to produce than a videotape). Eventually, DVD will be the one uniform recording format, replacing cassettes, DAT, videotape, and CD-ROM. A DVD drive is already virtually a standard item on computers, and the manufacturers claim that in a time of 3 years it has become the most successful electronics product of all time for home use (Figure 21.4).
Computers are the main end use of DVD at present, but DVD drives to replace videocassette players are already widely available. The spread of DVD as a replacement for VCR, however, is not likely to spread widely until the recording version reaches an acceptable price level. Surveys have shown repeatedly that the most common use for VCRs in the United Kingdom is to record TV programs either when the viewer is not at home or when two interesting programs are being broadcast at the same time. Use of DVD simply to play prerecorded discs is very restrictive—I cannot think of more than a handful of films I would ever want to see again, and some of my own videotapes have not been played since the day I recorded them. This is mainly a United Kingdom attitude, and the laser disc that was rejected in the United Kingdom has survived up until now in other countries.
● With the primary markets of computers and film viewing now being supplied, we are waiting for a standardized DVD format for audio that reportedly will allow up to 17 h of CD quality to be stored on a single disc.
DVD offers so much more storage space than CD that the options it allows are more than most users can cope with at first. A single-layer disc can store just over 2 h of digital video signals at a higher quality than is possible using VCR (which relies on considerable bandwidth reduction). More than one layer of CD recording can be placed on a disc, however, because the layers are transparent, and by altering the focus of the reading laser, it is not technically difficult to read either of two superimposed layers that are only a fraction of a millimeter apart.
By making two-layer DVDs the recording time can be doubled, and by adding double- sided recording it can be doubled again to 8 h of video. The discs can contain up to eight audio tracks, each using up to eight channels, so that films can contain soundtracks in more than one language and cater for surround sound systems.
The DVD can also end the concept of a film as a single story because, unlike tape, it can switch from one set of tracks to another very quickly, allowing films to be recorded with several options endings, for example. Different camera angles can also be selected by the viewer from the set recorded on the disc, and displays of text, in more than one language, can be used for audio and video tracks. Like CD and so unlike VCR, winding and rewinding are obsolete concepts, and a DVD can be searched at a very high speed that seems instantaneous compared to VCR. The disc is also smaller than a videocassette, does not wear out from being played many times, and resists damage from magnets or heat.
● DVD for video uses MPEG-2 coding and decoding, but there is nothing to prevent cut-price producers from coding with MPEG-1, producing the same video quality as a VCR. Even MPEG-2, however, is a lossy compression method, which sometimes shows in video quality as shimmering, fuzzy detail, and other effects.
● In contrast, DVD audio quality is excellent. DVD audio can optionally use CD methods (PCM) with higher sampling rates for even better quality than CD. Other options, used mainly in connections with films, are Dolby Digital or DTS- compressed audio.
Regionalization
Unlike audio CD, DVD is more regionalized than we would wish. Taking a cynical view, this is done to prevent European users from flying over to the United States to stock up with DVDs at bargain prices. Film studios have taken the same attitude to DVD as the record companies did to DAT—if you can’t ban it, cripple it. The official reasons are that regionalization prevents premature release of a file in another country and protects the distribution rights of suppliers in different countries. Regionalization does not apply to DVDs that consist purely of audio signals.
Apart from regional codes, DVDs must be designed to work with the type of color TV coding that different countries use, so that DVDs have to be manufactured in NTSC, PAL, and SECAM versions.
The DVD standard includes regional codes, and each DVD drive or deck is allocated a code for the region in which it is marketed. A disc bought in one region will not play on a deck/drive bought in another region, because the codes will not match. Several DVD users in the United Kingdom have countered this by buying their DVD equipment in the United States and then also buying the discs in the United States.
The established regions are:
1. United States, Canada, U.S. territories
2. Japan, Europe, South Africa, Middle East (including Egypt)
3. Southeast Asia, East Asia (including Hong Kong)
4. Australia, New Zealand, Pacific Islands, Central America, Mexico, South America, Caribbean
5. Eastern Europe (Former Soviet Union), Indian Subcontinent, Africa (also North Korea, Mongolia)
6. China
7. Reserved
8. Special international venues, such as airliners and cruise ships
The manufacturers of discs are not obliged to use these codes, and if they do not do so the discs can be used on any drive/deck anywhere in the world. Some types of drives/decks can be modified so that they will play DVDs irrespective of regional coding.
● DVD-ROM discs that are used for computer software are not subject to region codes, nor are audio DVDs.
Copy Protection
DVDs can use four different methods of copy protection systems. The Macrovision system includes signals that will cause a VCR to record incorrectly by feeding incorrect information to the synchronization and automatic level control circuits. CGMS is designed to prevent serial copying (making copies of copies). CSS (Content Scrambling System) is a form of data coding supported by film studios, but the coding algorithm has been cracked and posted in the Internet (along with methods for defeating other protection systems), casting doubt on the future of this method. Finally, the DCPS (Digital Copy Protection System) is designed to prevent perfect digital copying between devices that incorporate this coding system.
DVD-Audio
The first DVD drives started to appear around 1996, but at that time there was no agreed format for DVD-Audio, despite the obvious advantages of DVD for audio recording.
Considerable effort has gone into defining standards, but the final specification was approved in February 1999. Any delays were caused by the introduction of copy-protection codes as demanded by the music industry.
The situation now is that it is possible to design universal DVD players that will deal with both DVD-Video and DVD-Audio, but decks intended for DVD-Audio only will not play DVD-Video. As a further complication, because DVD-Audio is a rather different format, some DVD-Audio discs will not be fully usable in any DVD-Video player other than a universal type, which at the moment is not in production or even planned. With some cooperation from manufacturers it would be possible to turn out DVD-Audio discs that would operate on all DVD decks or drives. As usual, it is unwise to be a pioneer consumer, just as it was in the Beta/VHS days.
The protection system that has been adopted uses what the manufacturers call a digital watermark. This adds signals that appear as low-level noise, and the recording companies claim that this is completely inaudible. If enough audiophiles can hear the difference, then it is a distinct possibility that two separate audio markets could develop, one using the older CD format for music acceptable to enthusiasts, with DVD used for all other recordings. However, we may feel that the golden-eared brigade can always detect the inaudible, even on discs that have not had the coding added, but most users will not be affected.
● Sony and Philips, who developed the CD standards, have joined forces again to make their Super Audio CD format that competes directly with DVD-Audio. This takes us all back to the VCR battles of VHS and Beta, but manufacturers are likely to respond by making playing decks that will allow the use of either type of disc. At the moment, neither players nor discs are in plentiful supply.
Although DVD drives will read CDs, they will not in general read CD-R discs, and since recordable DVD is still rather distant, this might be a stumbling block to anyone who is contemplating transferring a treasured collection of tracks to CD-R. However, most DVD players can read CD-RW discs. This difference arises because DVDs use a laser whose light color is not the same as is used for CD players, and this light does not match that used for CD-R, although it is better adapted to CD-RW.
At present, I would not urge anyone to rush out and buy DVD-Audio, even if equipment becomes available on the United Kingdom market. The list of incompatibilities already suffered by DVD-Video (films that will not play on specific players) is very long, and we simply can’t guess how many problems of the same type we might see with DVD- Audio. For the long term, however, the medium must be the future of audio and video distribution. In the United Kingdom, much depends on making recordable DVD at a price that is not too much out of line with VCR, which is a tall order even when all TV is digital. As to DVD-Audio, its day will come when all record companies start to distribute on DVD rather than on CD.