The pregap on a Red Book audio CD 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 song In the field of Sound recording and reproduction, recorded music, a hidden track (sometimes called a ghost track or a secret track or an unlisted track) is a song or a piece of audio that has been placed on a CD, Compact Cassette, audio cassette, ...

s 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 quickly made obsolete in mid 1996 when an update to

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in driver SCSI1HLP.VXD made the pregap track inaccessible. It is unclear whether or not 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 ''

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or ''

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'' 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 or a secret track or an 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 wa ...

. 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.

Pregaps in CD-R media

{{further, Orange Book (CD standard)

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's Toast and a custom .cue file can provide a way around this. Ripping of pregap audio is supported by the application X Lossless Decoder.http://tmkk.pv.land.to/xld/index_e.html Windows: *

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provides the functionality to write to Index 0 Linux: *

cdrecord cdrtools (formerly known as cdrecord) is a collection of independent projects of free software/Open source software, open source computer programs, originally created by Eric Youngdale for Yggdrasil Linux/GNU/X, Yggdrasil Linux. The project ...

supports writing any kind of pregap *

cdrdao cdrdao (''“CD recorder disc-at-once”'') is a free software, free utility software product for Optical disc authoring, authoring and ripping of CD-ROMs. The program is released under the GNU General Public License, GPL. Cdrdao records audio o ...

cdrdao

supports writing any kind of pregap *

K3B K3b (from KDE Burn Baby Burn) is a Compact Disc, CD and DVD optical disc authoring, authoring application by KDE for Unix-like computer operating systems. It provides a graphical user interface to perform most CD/DVD burning tasks like creating a ...

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

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"Hot" ECD Audio engineering