MFDigital CD DVD Information Library
Thursday, July 08, 2004
Mixed Mode CD > Enhanced Music CD
Enhanced Music CD

Enhanced Music CDs are a type of mixed mode CD developed by Philips and Sony in conjunction with other companies such as Microsoft and Apple. Often referred to as CD EXTRA or CD Plus these discs contain two sessions. The first session contains up to 98 audio tracks; the second session contains the data track. When played on an audio player, it only sees the first session and so does not try to play the data session. The specification (the Blue Book) is based on the multisession pressed disc specification with some application specific additions for handling lyrics, titles and stills.

CD EXTRA discs, according to the Blue Book, are intended to be played on dedicated hardware as well as PCs. Therefore the data formats to be used are defined closely in a similar way to the White Book specification for Video CD. The main features of such discs are as follows.

Playable on a wide range of hardware including PCs under Windows 95, Macintosh computers, and dedicated CD Plus players (but not CD-i players which cannot play CD EXTRA discs).

Session one contains up to 98 tracks of audio data conforming to the Red Book specification.

Session two contains one track of CD-ROM XA (ie Mode 2) sectors and must include certain specified files and directories and use the ISO 9660 file system. For Macintosh compatibility, it is possible to make the data track include HFS as well as ISO9660. The following directories and files are required:

  • An AUTORUN.INF file in the root directory which meets the Windows 95 Autoplay specification.
  • A CDPLUS directory containing general information, lyrics and MIDI data.
  • A PICTURES directory containing pictures encoded in both MPEG and other formats.
  • An optional DATA directory containing additional data files depending on the application.

The CD EXTRA format is supported by Microsoft (who worked with Philips and Sony on the specification) and Apple. Both these companies have developed software tools to create CD EXTRA titles.

Mixed Mode CD > CD-ROM Ready
CD-ROM Ready

This is one name for mixed mode discs where the data 'track' is hidden in the pause before track 1 (an audio track) begins. This avoids the problem of trying to play track one when it contains data. However, it is still possible for audio players to attempt to play the data if the user 'rewinds' into the data and then plays it.
A number of so-called Enhanced CDs or ECDs are actually of this format and not CD Extra discs.

Another type of mixed mode disc, where the same problem has been partly solved in a similar way, is the CD-i Ready disc. This is a CD with the CD-i data hidden in the pause preceding the audio tracks. However, there are some problems with this approach and Philips have never confirmed the current tentative specification.

Mixed Mode CD > Data in Track 1
Data in Track 1

The first track of a CD can be a CD-ROM data track. The producer of such discs can get the benefits from two titles but only needs to produce one. The user with only a CD audio player, should be unaware of the data content, while the user with a CD-ROM drive in a PC will be able to play the audio and use the data. Applications include the addition of sleeve notes with graphics/photos plus more interactive and esoteric applications.

One of the problems which has inhibited the widespread use of mixed mode discs is that some early CD players will try to read a data track with possibly disastrous consequences. This 'track one' problem has prompted a number of different solutions including CD-ROM Ready and CD EXTRA discs.

Mixed Mode CD > What is Mixed Mode?
CD audio and CD-ROM discs usually contain 1 or more tracks of the same mode, ie one of the following:

Mixed mode discs comprise a combination of tracks of different modes, usually one data track (mode 1 or mode 2) plus up to 98 audio tracks.

Since the Red Book was written at a time when CD-ROM was not considered, mixed mode can cause problems when playing on audio players. In particular, it is important to prevent audio players trying to play the data track(s).

Only one of the mixed mode formats, CD Extra or Enhanced Music CD, ensures that CD audio players do not play the data, but there are problems running these discs on older CD-ROM drives.