The pregap on a Red Book

audio CD Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio compact discs. The standard is defined in the '' Red Book'' technical specifications, which is why t ...

is the portion of the audio track that precedes "

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01" for a given track in the table of contents (TOC). The pregap ("index 00") is typically two seconds long and usually, but not always, contains silence. Popular uses for having the pregap contain audio are live CDs, track interludes, and hidden songs in the pregap of the first track (detailed below).

Unconventional uses of the pregap

Computer data in pregap

The track 01 pregap was used to hide computer data, allowing computers to detect a data track whereas conventional CD players would continue to see the CD as an audio CD. This method was made obsolete in mid 1996 when an update to

Windows 95 Windows 95 is a consumer-oriented operating system developed by Microsoft and the first of its Windows 9x family of operating systems, released to manufacturing on July 14, 1995, and generally to retail on August 24, 1995. Windows 95 merged ...

in driver SCSI1HLP.VXD made the pregap track inaccessible. It is unclear whether this change in Microsoft Windows' behavior was intentional: for instance, it may have been intended to steer developers away from the pregap method and encourage what became the Blue Book specification "CD Extra" format.

Hidden audio tracks

On certain CDs, such as '' Light Years'' by

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, '' HoboSapiens'' by John Cale, or '' Factory Showroom'' by

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, the pregap before track 1 contains a

hidden track In the field of recorded music, a hidden track (sometimes called a ghost track, secret track or unlisted track) is a song or a piece of audio that has been placed on a CD, audio cassette, LP record, or other recorded medium, in such a way as t ...

. The track is truly hidden in the sense that most conventional standalone players and software CD players will not see it. Such hidden tracks can be played by playing the first song and "rewinding" (more accurately, seeking in reverse) until the actual start of the whole CD audio track. Not all CD drives can properly extract such hidden tracks. Some drives will report errors when reading these tracks, and some will seem to extract them properly, but the extracted file will contain only silence. Other CDs contain additional audio information in the pre-gap area of other tracks, resulting in the audio only being heard on a conventional CD player if the CD is allowed to "play through," but not if you jump to the next track. Some CDs also contain phantom tracks consisting of ''only'' index 0 data, meaning the track can only be played on a conventional CD player by allowing the CD to play through a previous track to the next track.

Pregaps in CD-R media

OS support

Mac OS X: Currently does not support more than a 2-second pre-gap in the first track under its CD burning utilities. Using a combination of Roxio Toast and a custom .cue file can provide a way around this. Ripping of pregap audio is supported by the application X Lossless Decoder. Windows: * Exact Audio Copy provides the functionality to write to Index 0 Linux: * cdrecord supports writing any kind of pregap *

cdrdao cdrdao (''“ CD recorder disc-at-once”'') is a free and open source utility software application for authoring and ripping of audio and data CD-ROMs. It is licensed under GPL-2.0 or Later. The application is available for several operatin ...

supports writing any kind of pregap * K3B, a frontend for several CD/DVD burning/ripping utilities, supports hiding the first track in the pregap of the second one.

Notes

External links

Technical Specifications
of the Squirrel Nut Zippers "Hot" ECD {{Compact disc Audio engineering Compact disc