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In the field of recorded music, a hidden track (sometimes called a secret track) is a song that has been placed on a CD, audio cassette, LP record, or other recorded medium, in such a way as to avoid detection by the casual listener. In some cases, the piece of music may simply have been left off the track listing, while in other cases more elaborate methods are used. In rare cases a 'hidden track' is actually the result of an error that occurred during the mastering stage production of the recorded media.
A vinyl record may be double-grooved, with the second groove containing the hidden tracks. Examples of double-grooving include Monty Python's 'three-sided' Matching Tie and Handkerchief, Tool's Opiate EP, and Mr. Bungle's Disco Volante.
On indexed media such as compact discs, double-grooving cannot be used, but there are additional methods of hiding tracks, such as:
- Similar to the above example, having the song as a separate unlisted track with its own index point.
- Placing the song after another track (usually, but not necessarily, the last track on the album), following a period of silence. For example, Nirvana's song Endless, Nameless was included as a hidden track in this way on their 1991 CD Nevermind, after 10 minutes of complete silence. Although it was not the first hidden track to use this technique, this hidden song gained significant attention.
- Placing the song in the pregap of the first track, so that the CD must first be cued to the track, and then manually back-scanned; these are often referred to as Track 0 or Hidden Track One Audio (HTOA). A CD player will not play these tracks without manual intervention, and some models (including computers) are unable to read such content. On Super Furry Animals third album, Guerrilla, The Citizens Band is found in the pre-gap approximately 5 minutes before the beginning of track 1. The song's lyrics are printed on the interior of the cardboard outer sleeve of the CD, essentially rendering them inaccessible without taking the sleeve apart. See List of albums with tracks hidden in the pregap.
- Placing the song in pregaps on other tracks on the album.
- Using many short tracks of silence before the hidden track. On Lazlo Bane's debut album 11 Transistor, the eleventh song, Midday Train, is followed by 57 silent tracks 4 seconds each, with Prada Wallet (sometimes referred to as The Birthday Song) being the 69th track on the album. The total length of silence between the two songs is 3:48.
- Making the track playable only through a computer, such as the '15th' track on Marilyn Manson's Mechanical Animals album, which can only be accessed through an Enhanced CD executable.
- Hide the song in a mixed or distorted way which must be undone to play it. For example, on a DVD included with the deluxe and 'ultra-deluxe' editions of Nine Inch Nails's Ghosts I–IV, two hidden bonus tracks (37 Ghosts and 38 Ghosts) are included as digital multitrack files, from which the songs may be reconstructed.
It is occasionally unclear whether a piece of music is 'hidden'. For example, Her Majesty, which is preceded by fourteen seconds of silence, was originally unlisted on The Beatles' Abbey Road, but is listed on current versions of the album. This is one of the first instances of a hidden track. The song snippet at the end of Sgt. Pepper's Lonely Hearts Club Band is considered by some to be a hidden track, by others to be noise not worthy of such a designation, and by others to be part of A Day in the Life.
- Aaliyah's self-titled album Aaliyah features the hidden song Messed Up on track 15. During the stages of the album creation, Aaliyah had no desire to put this song on the album, but after numerous inquiries from different labels and colleagues, she decided on making it a hidden track.
- In some rare cases, it is used to avoid legal issues. An example is Ramones' Loco Live American version, which has the song Carbona Not Glue hidden after Pet Sematary on track 17. It was originally recorded on their album Leave Home, but the makers of the spot remover Carbona, a registered trademark, objected. Therefore, reference to the song was removed from the album and cover.
- Freedom by Paul McCartney was a hidden track on the original release of Driving Rain. It was later added as a track on the re-release. The track was not meant to be hidden; it was a tribute to 9/11 victims, and McCartney wanted it on the album. The artwork was already done, so it was a hidden track.
- Train in Vain by The Clash, which appears at the end of London Calling, was left out of the vinyl's track listing simply because it was a last-minute addition to the album, when the sleeves were already printed. It is thus not a real hidden track. It was originally intended as a promotional giveaway for NME. The later CD versions list the track on the sleeve.
- Green Day's All By Myself (by drummer Tré Cool) was added as a secret song to Dookie due to the low sound quality of the original live recording.
- "Weird Al" Yankovic's Bite Me from the album Off the Deep End was put on after ten minutes of silence to scare listeners who had forgotten to turn off the CD player. In fact if you play the song backwards and slow it down by 800 percent, a distorted clip of the song Tears of the Earth by David Hallyday can be heard. It was also a loose parody of Endless, Nameless by Nirvana. The cover of Off the Deep End is also a parody of the album containing that track, Nevermind, and its first track is a parody of that album's first track, Smells Like Teen Spirit.
- The X-Files: The Album, features a hidden track at 10 minutes and 13 seconds into the final track. The track consists of series creator Chris Carter explaining the series mythology and meaning behind the alien conspiracy. The hidden track even includes spoilers and minute details in the show's overall plot that had not yet been resolved on the show itself when the album was released. This track was included as both a surprise to devoted fans who would seek out answers in cross-promotional merchandise, and as a mystery to new fans who would need to watch the show more closely to better understand the track.
- Eugene Mirman's album The Absurd Night Club Comedy of Eugene Mirman includes a hidden track making fun of hidden tracks, and telling the listener that he or she has a very bizarre mission.
- The Jam's All Mod Cons does not list the song English Rose and its lyrics on original vinyl copies because Paul Weller believed the title and song lose meaning without accompanying music. They have been added to re-releases of the album.
- Skip Spence's Land of the Sun was included as a hidden track by producer Bill Bentley to specifically close a tribute album to Spence, More Oar: A Tribute to the Skip Spence Album.
- Oasis' compilation album, Time Flies, features the single Sunday Morning Call as a hidden track. The album was an anthology of all of the band's singles, but principal songwriter Noel Gallagher openly detests the song, so chose to have it hidden.
Sometimes hidden tracks have become well known and received radio airplay, and occasionally climbed the charts.
- The Beatles' track Her Majesty from their 1969 album Abbey Road is considered a hidden track, though it was originally a part of the album itself, before Paul McCartney requested that it be removed; the song was later inserted at the end of the master recording after 20 seconds of silence, because the producers were not willing to remove it entirely from the album. The original pressings of Abbey Road did not list Her Majesty on the back cover song title listing, nor the record label; subsequent LP pressings and then CD issues were issued revealing the track. However, two years prior, in 1967, on the UK version of the Sgt. Pepper's Lonely Hearts Club Band album, there was the inner groove that appeared after A Day in the Life at the end of side 2. It was an unexpected, untitled, and un-credited Beatles recording; so this might be deemed a precursor to the hidden track. A potential hidden track on yet another Beatles album is on The Beatles (also known popularly as The White Album) 1968 double album. The hidden track is a snippet of a song called Can You Take Me Back, serving as an 'outro' to Cry Baby Cry.
- Janet Jackson's track Whoops Now, a hidden track from her album janet., was released as a single, and reached number 9 in UK Singles Charts, and number 1 in New Zealand Singles Chart.
- The Rembrandts had a sudden radio hit in 1995 with I'll Be There For You, the theme song to Friends, so it was added at the last minute to their third album LP. As a result, the song was a hidden track on the early printing, since the CD packaging had already been completed by the time the song was added. A sticker was however added to the outer shrink wrap advising the song's inclusion.
- Eels' album Daisies of the Galaxy contains a hidden track, Mr. E's Beautiful Blues, which was released as a single, and received radio airplay, although it was not featured on the sleeve notes. The song was, in fact, released as the first single from the album, and peaked at number 11 on the UK Singles Chart.
- Cracker's Euro-Trash Girl, an original, was one of their biggest radio hits, despite being a hidden track on Kerosene Hat.
- Skin (Sarabeth) by Rascal Flatts, a hidden track from their 2004 album Feels Like Today, received enough airplay to chart in the Top 40 on the country charts, peaking at number 2 in late 2005. In mid-2005, the album was re-issued, with the song officially listed as a track, coinciding with the song's release as a single.
- Of the two hidden tracks on Lauryn Hill's The Miseducation of Lauryn Hill, one of them, the cover of Can't Take My Eyes Off You was nominated for a Grammy in 1999 in the category of 'Best Female Pop Vocal Performance'. It was the first time a hidden track was nominated for a Grammy.
- One of the hidden tracks on P!nk's fourth album, I Have Seen The Rain, gained significant attention by P!nk fans, as her father, James T. Moore was featured on the song.
- Peter, Paul and Mary's 2003 album, In These Times, revealed that after 30 seconds of silence from "Oh, Had I a Golden Thread, there was a hidden live track of a Spanish folk song Mi Caballo Blanco,although it was listed in the box-set Carry It On. The track was later officially listed on their 2014 album: Discovered: Live in Concert 
- Easter egg (media)
- List of albums containing a hidden track
- List of albums with tracks hidden in the pregap
- Bonus track
- Track (CD)
- Sampling (music)
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