** Various artists, “Rarewerks,” Astralwerks.

Such acts as Fatboy Slim, Chemical Brothers and Air have given the Astralwerks label the cachet to put out a compilation featuring previously unreleased tracks from its artists. As this CD frequently reminds us, there is a reason these collections are not usually released to the public. While there are occasional high points, such as Q-Burns Abstract Message’s airy, jazz-tinged “Feng Shui” and the Basement Jaxx’s fiery, Spanish-flavored “Bingo Bango,” at least half of the tracks should have remained rare.

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Albums are rated on a scale of one star (poor), two stars (fair), three stars (good) and four stars (excellent). The albums are already released unless otherwise noted.