Since its introduction in the early 1980's, the compact disc has become the chosen format for millions of music listeners. Due to its digital recording, the fidelity produced is of the highest quality and the disc itself is near indestructible. The same technology makes the CD an attractive medium for transporting other types of digital information. Not only are compact discs extremely reliable but large quantities can be reproduced quickly and inexpensively.

Because of the phenomenal growth of CDs and technology as a whole, new CD formats have evolved and been defined. The basic CD standards and principles are defined in the Red Book (audio), Yellow Book (CD ROM), Orange Book (CD-R), and Green Book (CD-I). All other technologies, whether an official standard or not, are derived from the principles defined in these original industry books.

Most new formats are being introduced as a "multi-media" solution. Multimedia is simply a blend of media types: audio, text, graphics, and/or video that is being delivered all on one medium. Multimedia is important because it allows us to mix what can be considered as separate and distinct media or one medium. Information can be combined from various sources: books, films, periodicals, LPs, cassettes, computer software, etc. Record companies can produce CDs that not only contain audio recordings, but can also include animation, graphics, text, and video that further complements the artistic expression and adds additional consumer value. The consumer may choose to use all in combination or only a chosen part. It is from this direction that the formats discussed in this paper originate. There are many variables and considerations in introducing a new CD format, i.e., hardware (players), software, market demand, etc.. This paper attempts to discuss the various formats in CD technology, with the advantages, disadvantages and the requirements of each. The compact disc formats that will be discussed are as follows: Mixed Mode, Hidden Track, Stamped Multisession (CD-Extra), CD-I, and CD+G.

A Mixed Mode CD (see Diagram A) is a CD that contains ROM data in track 1 and is followed by up to 98 audio tracks. A ROM drive will play a disc’s first track which in this case contains ROM data. Appropriate software drivers and/ or software may be required on a computer to play the remaining audio tracks. Audio players are capable of playing the audio tracks. Audio players also have access to the first track that contains ROM data. If the audio player is not capable of muting the ROM track when it is attempting to play, a blast of static sound will most probably occur and cause severe speaker damage.

Advantages

The audio tracks are playable on an audio player. The ROM track is fully compatible with ROM drives. The audio portion may be played on ROM drives as well with the appropriate software.

Disadvantages

When the ROM track (track 1) is played on a non-muting audio player, full volume static will be heard which can be damaging to audio equipment. To prevent this, you must immediately skip to track 2 which starts the audio tracks.

Diagram A: Mixed Mode Layout

This is a non-standard format developed to compensate for the non-muting audio players that would play a ROM track as full static. The Hidden Track formatted disc (see Diagram B) is designed to play in a ROM or audio player. The ROM data is contained in Track 1, index 0 and the audio tracks begin at Track 1, index 1. Most audio players initialize at Track 1, index 1, so the ROM track is "hidden" to the audio player. ROM drives, with the appropriate software drivers installed, can access the ROM track from index 0 of track 1.

An audio track can also be placed in index 0 of track 1. This format allows the consumer to "back-up" or rewind into the hidden track on the audio player and listen to the audio track. This hidden audio track will not be played automatically by the audio player when the disc is inserted. If the audio player allows you to back-up into index 0 of track 1 and it contains ROM data, this may result in the full volume static problem described in Mixed Mode CD section of this paper. The blast of static could be damaging to audio equipment.

Advantages

Audio players will play the audio tracks. Most non-muting audio players will not play the ROM data as full static. The ROM track can be played on most Macs and Windows 3.1 PCs with the appropriate software drivers installed.

Disadvantages

Most Macs do not need additional software to read this format but Windows 3.1 PCs may need software driver upgrades. More recent Windows 95 drivers do not allow access to Track 1, Index 0 because Microsoft supports another Enhanced CD format. Some audio systems allow the consumer to rewind or back up into the ROM data giving the opportunity to play the full static which can damage speakers. Because Hidden Track is non-standard, CD-Rs cannot be made. Replicated disc samples are required as proof discs for customers, making premastering more expensive than other options.

Diagram B: Hidden Track Layout

Stamped Multisession is a format that solves the problem of having ROM data in Track 1. There are two sessions on a disc where audio is contained in session 1 and ROM data is contained in session 2 (see Diagram C). Audio players only see what is in session 1, thus solving the problem of playing full volume static on some audio players. Multisession hardware and software drivers are required on a PC to access the ROM data in the second session.

There is a Yellow Book multisession specification and another specification known as the Blue Book which covers CD Extra. CD Extra achieves the same as the Yellow Book multisession specification except that it requires special software for premastering and the payment of royalties since it is a Sony/Philips proprietary format. Microsoft supports the CD Extra Blue Book format with its Windows 95 operating system.

Advantages

Audio players cannot access the ROM data so the playing of full static is not an issue. Audio players can access the audio tracks like any Red Book audio disc.

Disadvantages

Multisession capable hardware and software must be installed on the computer to access the ROM data. Most drives made before 1995 are not multisession capable. Older operating systems, like Microsoft’s Windows 3.1, may not have multisession capable drivers available.

Diagram C: Multisession & "CD Extra" Layout

(Only two (2) sessions are shown in this example)

Compact Disc Interactive (CD-I) is a proprietary format developed by Philips for consumer use on CD-I players. The CD-I format (See Diagram D) is defined in the industry standard Green Book. The CD-I disc is composed of a CD-I track or tracks and may be followed by one or more CD-DA (Compact Disc Digital Audio) tracks. The first track on a CD-I disc must be a CD-I track. All other tracks may be used for CD-I tracks or CD-DA tracks.

CD-I players connect to your television set in a manner closely resembling the connection of a VCR (Video Cassette Recorder). CD-I applications vary but include developed titles for education, training, video, games, and other areas of interest where you need to present video, graphics, text and audio to a consumer audience having access to a TV and CD-I player. You must obtain appropriate authoring software if you wish to build a CD-I disc.

Advantages

The audio tracks on a CD-I will play in an audio player. CD-I players will plug into virtually any television set any where in the world; this is a world-wide standard.

Disadvantages

The first track will be a data track. This track must be skipped in order to play the audio on an audio player. If the player does not mute the data track, the speakers could be damaged.

Diagram D: CD-I Layout

This is a standard audio disc that contains a limited amount of graphics in defined subcode channels. This disc works in all audio players but the graphics portion is only available in a special CD+G or Karaoke player.

Advantages

A CD+G CD can be sold as a basic audio CD with the added features of having displayable graphics that can be viewed with the appropriate equipment.

Disadvantages

CD+G graphics can only be viewed with a CD+G compatible player. A CD+G disc must be created with special authoring software. Only a very small amount of data can be stored as graphics in the appropriate subcode channels.

As you may now conclude, the basic Compact Disc format developed by Philips and Sony allows for tremendous variation, thus creating opportunity to use this durable and versatile medium for innumerable formats and platforms. Whatever your Compact Disc application, there are format choices currently available and more are being developed. As the industry evolves, some formats will become dominant in the market while others may have only limited value.