Mixed Mode CD

A mixed mode CD is a Compact Disc which contains both data and audio in one session. Typically the first track is a data track while the rest are audio tracks. The most common use for mixed mode CDs is to add CD-quality audio to video games on a CD.

The term "enhanced CD" is sometimes used to refer to mixed mode CDs, though it is most commonly used to refer to either a more general category of formats that mix audio and data tracks, or to the particular Enhanced Music CD format.

Mixed mode CDs are implicitly described in the original CD-ROM standard (the Yellow Book, later standardized as ISO/IEC 10149 and ECMA-130), which allows a CD-ROM to contain only data tracks, or data tracks and audio tracks. The CD-ROM standard, however, does not mention the term "mixed mode", nor does it describe any particular order of data and audio tracks on the disc. Since the original CD-ROM standard did not support multiple sessions, mixed mode CDs are created using only one session.

Some CD players from the 1990s have trouble with the mixed mode CD format because the first track, which contains data, might be "played", resulting in screeching which, at worst, might damage speakers. This is caused by the player not recognizing the "data" flag bit for the track that distinguishes it from an audio track; these players were designed for audio CDs only, with no provisions to handle CD-ROMs with data and audio tracks. Newer audio CD players do check for data tracks and (at least) mute the track if it contains data and not audio.

Several newer formats were created to improve the usability of CDs with audio and data tracks in audio CD players; these formats include CD-i, CD-i Ready and the Enhanced Music CD format. In the case of the Enhanced Music CD format (also known as CD Extra/CD Plus), audio tracks are placed in one session before the data tracks, which are stored in a second session. This avoids the problem with the data track for most audio players, since they will only be able to recognize the first session.

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