The Compact Disc — that integral piece of our music and data lives — is governed by a series of published specifications named for the colors of their book covers. The first specification — the venerable Red Book — defines the physical characteristics and data format of the CD, as well as its use for music (which originally was its only use).
As other applications were developed, the practice of naming the specs after colors was continued to include yellow, orange, green, white, and blue. Eventually that practice was discontinued, presumably because no one wanted to be responsible for the Mauve Book. The six books named after colors (see Fig. 1) define the core technologies of CD, CD-ROM, and recordable CD, as well as the application formats CD-I, Video CD, and Enhanced Music CD (also called CD Extra). These standards, and additional specifications (no longer named after colors), are maintained by Sony and Philips Electronics, the originators of the CD format.
You may be wondering if you can go to Amazon and order the Red Book and other CD specs. The answer is no — access to the books is carefully controlled. General access to the specifications requires a $5,000 fee up front to Philips Intellectual Property and Standards (www.licensing.philips.com) and a stiff confidentiality agreement. However, the original Red Book eventually became ISO/IEC standard 60908. The PDF version can be purchased at www.iec.ch for 263 Swiss Francs (around U.S. $200).
For this article, I will cover the Red, Yellow, Orange, Green, White, and Blue books. Super Audio CD (SACD) will not be covered because it is not considered a CD format. SACD is truly a different beast and deviates from the physical spec of formats derived from Red Book.
RED BOOK (CD DIGITAL AUDIO)
Red Book defines the physical parameters of the CD as well as data formatting and track addressing for audio CDs. Audio CDs are often referred to as Red Book discs; however, all CDs must conform to the Red Book definitions of format and basic storage. Physical parameters defined by Red Book include dimensions of the disc, the size and spacing of pits, and the requirements for the optical pickup to read the disc.
Red Book also defines how data is stored on the disc. You might think a CD contains data bits and bytes arranged in a straightforward manner. In fact, data is arranged according to a carefully defined scheme, called 8-to-14 modulation, wherein each 8 bits of original data becomes 14 bits on the disc and includes redundancy and check codes.
Data bytes are shuffled so that sequential bytes are placed on nonadjacent sectors of the disc. This ensures that a scratch or other physical defect will not wipe out a large contiguous block of original data, which would make the disc unusable.
That processing is designed to compensate for the inherent limitations of reading dense data at a high speed. Any optical disc, in any particular drive, exhibits a block-error rate. Damaged discs or media that are marginally compatible with the drive have a high block-error rate. Red Book specifies the maximum block-error rate before reading problems become evident to the user.
Subcode information is also embedded in the data stream. On audio CDs, subcodes are used to carry timing information as well as optional embedded graphics and text.
Red Book defines the storage format of audio for playback on standard CD players. That includes the now-familiar digital-audio coding parameters — linear pulse code modulation (LPCM), sample resolution of 16-bit stereo, and a sampling rate of 44.1 kHz.
Red Book provisions for low-level formatting have proved to be both a boon and a bane. Data is contained on a single spiral track, like the groove on a phonograph record, with a table of contents that contains pointers to every track. That method of track addressing is inadequate for computer applications. In addition, the original provisions for error detection, error correction, and sample interpolation (called concealment) are not suitable for critical data.
YELLOW BOOK (CD-ROM)
As the audio CD gained market acceptance, technologists went to work creating a comparable standard for CD-ROM. That standard became Yellow Book.
It was decided to keep the basic physical and data storage formats of the disc from Red Book. To provide the extra data protection needed for CD-ROM, Yellow Book redefines the arrangement of data on the disc, splitting it in to sectors of 2,352 bytes compared with 2,048 bytes for audio CDs. The additional 304 bytes of each sector are dedicated to error correction and addressing.
CD-ROM data may be stored as Mode 1 or Mode 2 data. Mode 1 provides the extra error detection and correction that is needed for software and critical data. Mode 2, without the additional correction, is better suited to media because the increased sector size makes it faster to read in a stream of data. Mode 2 is also more easily adapted for use on dedicated, noncomputer hardware.
Yellow Book defines data formatting for CD-ROM applications, but it doesn't address file systems and data retrieval in a computer environment or multimedia application. Two specifications that are not named after colors address those topics. CD-ROM XA is a Yellow Book extension that defines video and audio data interleaving and is the first CD spec that provides information regarding the use of data-compressed audio. It also defines how to place Red Book CD audio on a separate track of a CD-ROM disc.
CD-ROM XA became the basis for the CD-i Bridge specification, adding an ISO 9660 file system and providing for compatibility with set-top players. Several other extended-media CD formats are based on CD-i Bridge.
ORANGE BOOK (CD-R, CD-RW)
Orange Book (see Fig. 2) Parts II and III are multivolume documents that govern writable and rewritable CD formats. Part I describes Magneto-Optical CD drives, which never became as popular as CD-R. Orange Book Part II covers write-once CD-R, while Part III covers rewritable CD-RW.
Orange Book focuses on the physical aspects of a writable medium that is compatible with the original CD specification. It includes specifications for pregrooved blank discs that provide tracks for recording data. It also includes definitions of spot dimensions, tolerances, and reflectivity, as well as definitions for data organization and linking in multisession and hybrid discs.
In Orange Book Part II, CD-R discs are defined as compatible with standard replicated CD audio and CD-ROM discs. Orange Book Part III specs require that the drive be adapted to the CD-RW format, as are most CD-ROM drives manufactured today.
Physical compatibility of recordable CDs has turned out to be an ongoing vexation. Data can be written on a disc in many ways, utilizing different materials and writing methods. Each produces a different set of tolerances in spot-track dimension and before-after reflectivity.
GREEN BOOK (CD-I)
With the multimedia-optimization definitions of the CD-ROM XA spec in place, the CD technology community (Philips especially) became enamored with the possibilities of standardized interactive media. The result was the Green Book CD-interactive (CD-i) specification, which defines not only the disc format and data coding, but also the CD-i content and programming details. Green Book is the forerunner of the video Application Layer concept used in DVD Video.
CD-i was launched with great fanfare in 1986. Philips put tremendous energy into promoting the medium and in creating systems for content development. However, the first players did not hit the market until 1990, and even then there was a lack of compelling content. Philips and its partners kept up the fight for several years, but the format eventually sank from view as a consumer medium.
WHITE BOOK 2.0 (VCD, SVCD)
The Video CD (VCD) defined by the White Book 2.0 specification is the most successful consumer product of which no one in North America has ever heard. A forerunner to DVD, Video CD provides 74 minutes of MPEG-1 video and audio, with a menu for track selection.
When VCD came into existence, DVD was already on the drawing boards. Because VHS was a mature product in North America and Europe, the market makers concluded that Video CD offered little to attract Western viewers. The picture quality is not as good as moderate-quality VHS (despite claims to the contrary), and the limited playing time results in a lot of disc changing.
At the same time, VHS had not penetrated Asia, and there was a huge CD production capacity available in that area. Asian consumers thought VCD looked fine since they had less with which to compare it. VCD players and discs could be produced for much less than VHS. Track jumping and menu selection — two VCD features — also made it well suited for karaoke, which is massively popular throughout Asia.
VCD became a major hit in China and other East Asian countries. Even today, it is the video medium of choice in that market, while DVD is a premium format and VHS is scarcely present.
The hold of VCD on the Far East market has been strengthened by Super Video CD (SVCD). The development of SVCD was backed by the Chinese government, and although it is not part of the White Book specification, it is supported as a Sony-Philips standard. SVCD takes Red Book one step further by defining variable-speed playback, which allows the disc to carry medium-resolution MPEG-2 at bit rates of as much as 2.6 mbps. (The DVD rate is typically 5 mbps or higher.)
BLUE BOOK (CD EXTRA)
In the '90s, record labels and recording artists wanted to add CD-ROM data to their music CDs. While CD-ROM XA made it possible to combine audio and CD-ROM data tracks, it also created problems of player compatibility.
Orange Book included specifications for multisession recording. Red Book audio can be recorded in a first session, playable by standard audio CD players. A second session can consist of multimedia data that is readable by a computer or by a suitable dedicated player.
Although Orange Book defined multisession capability for recordable discs, the Red and Yellow books only provide for the mass manufacture of single-session discs. A new specification was needed before such enhanced CDs could become a medium of distribution, and thus the Blue Book was born. Blue Book is a specification for a stamped version of the Orange Book recorded multisession disc.
At first, there was great enthusiasm for Blue Book, but the effort ultimately foundered. Multisession discs required major changes to the mastering equipment, and it took time for the makers of production components to catch up.
In addition, when Blue Book was released, most drives could not read multisession discs. Eventually, interest waned as other means of combining high-fidelity music and multimedia came to the forefront. As a commercial product, Blue Book is now effectively dead.
RED BOOK EXTENSIONS (CD+G, CD TEXT)
From the beginning, Red Book defined a type of auxiliary data on the CD disc called subcode. That extra data accompanies the audio payload of every audio CD.
Subcode data is available in two areas of the disc. The lead-in provides about 5,000 bytes of subcode loadable when the disc begins to spin. A larger amount of data (approximately 31 MB total) is available in the program area, but it can be extracted only on the fly as the disc is read.
The first use of subcodes to carry extra information was CD+Graphics (CD+G), which included low-resolution graphic information readable by a suitably equipped player. The application for which it was most commonly used was karaoke, and many CD+G players were sold in Asia. In addition, an extension to the spec provided for MIDI data, but I don't know of any instance in which it is being used.
CD Text has more recently come into existence. Since 1997, every disc produced by Sony Music has included CD Text information, including album and track titles as well as the artist's name. Today, more and more audio CD players (hardware and software) read and display this information. CD Text is now an established part of the audio CD world.
The Photo CD is also worth noting, if only because its parent, Kodak, has made it available at almost every photo counter in the world. Photo CD is a content definition sitting on top of the CD-i Bridge format. The format is now somewhat dated, but Kodak's ubiquitous presence has given it a long life.
Gary S. Halllives in the tropical paradise of Hua Hin, Thailand. You can by visit his Web log athttp://garyinthailand.blogspot.com.
FOR FURTHER INFORMATION
The Internet offers a wealth of information on CD standards and specs. Below are links to get you started:
The official source for all of the CD specification documents, colored and uncolored.
An excellent information site from Disctronics, a major replicator based in the UK. There are links to separate pages for CD Audio and CD-ROM, as well as DVD and other formats.
Consultant Dana Parker maintains this site that has information and history about all optical media formats.
www.ncf.carleton.ca/~aa571/cdtext.htm and www.jbum.com/jbum/sware/cdg_revealed.txt
These sites have information about two related areas: CD Text and compact disc and graphics.
An excellent article on the history and politics behind the Super Video CD specification.
A search for books about “compact disc” at Amazon.com yields 11,825 items. Below is a list of recommended titles. Those that are out of print or out of stock are often available used.
The Compact Disc Handbook, by Kenneth C. Pohlmann (A-R Editions, 1992)
Compact Disc Technology, by Heitaro Nakajima (Ohmsha, 1992)
The CD-ROM and Optical Disc Recording Systems, by E.W. Williams (Oxford University Press, 1994)
The CD-ROM Book, by Jeff Sloman, Steve Bosak, and Joel Sloman (Que, 1994)
Digital Audio and Compact Disc Technology, by L. Baert, Luc Theunissen, Guido Vergult, and Jan Maes (Books Britain, 1995)