Octavarium is the eighth studio album by American progressive metal/rock band Dream Theater. Released on June 7, 2005, it was the band's final release with Atlantic Records. Recorded between September 2004 and February 2005, the album holds the distinction of being the last album ever recorded at The Hit Factory in New York City. With Octavarium, the band decided to create "a classic Dream Theater album", drawing upon their various stylistic influences while trying to make the music less complex. The album takes its creative concept from the musical octave.

Octavarium peaked in the top five in the Finnish, Italian, and Swedish charts, and in the top ten in the Dutch, Japanese, and Norwegian charts. Critical reception of the album was generally positive; the diversity of the music was praised, although critics found some of the songwriting to be inconsistent. Dream Theater promoted the album on a year-long world tour, with the majority of concerts lasting almost three hours and featuring a different setlist each night. The tour finished at Radio City Music Hall accompanied by an orchestra; this performance was recorded and released as a live album and concert video entitled Score. They co-headlined the 2005 North American Gigantour with Megadeth.

After completing a North American tour supporting one of their main influences, Yes, in summer 2004, Dream Theater took a two-month break. The band reconvened at The Hit Factory in New York City in November 2004 to begin work on their eighth studio album. The Hit Factory, a studio in which artists such as Michael Jackson, Madonna, Stevie Wonder, U2 and John Lennon had recorded, was earmarked for closure. Dream Theater was the last band to record there before it was permanently closed.

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