Titled "Ghosts I-IV," the collection comprises 36 tracks that total almost two hours. Reznor composed and recorded the set over a 10-week period last fall, along with help from producers Atticus Ross and Alan Moulder (Depeche Mode), with whom he has worked in the past. Touring NIN keyboardist Alessandro Cortini, veteran musician Adrian Belew, and Dresden Dolls drummer Brian Viglione also contributed, according to the album's website.

"This music arrived unexpectedly as the result of an experiment," Reznor wrote in a message posted at the site, which he launched Sunday night (3/2) after weeks of teasing fans with brief messages that hinted at a forthcoming project of some sort. "The rules were as follows: 10 weeks, no clear agenda, no overthinking, everything driven by impulse. Whatever happens during that time gets released as ... something.

"We began improvising and let the music decide the direction," he continued. "Eyes were closed, hands played instruments and it began. Within a matter of days it became clear we were on to something, and a lot of material began appearing. What we thought could be a five song EP became much more. ...

"The end result is a wildly varied body of music that we're able to present to the world in ways the confines of a major record label would never have allowed--from a 100% DRM-free, high-quality download, to the most luxurious physical package we've ever created."

Reznor, who earlier this year tested the waters of online distribution by offering up the Reznor-produced Saul Williams album "The Inevitible Rise and Liberation of Niggytardust," is allowing fans to download the first nine songs from "Ghosts I-IV" for free via NIN's website.

Fans looking to get all three-dozen cuts have several choices: $5 for all tracks in one of several high-quality digital formats; $10 for a two-CD set housed in a six-panel digipak with a 16-page booklet; $75 for a deluxe edition package that features a large fabric slipcase containing two embossed, fabric-bound, hardcover books, the two audio CDs, as well as a DVD containing multi-track versions of all 36 tracks, and a Blu-ray disc containing stereo mixes of the entire set; and $300 for an ultra-deluxe limited edition package that includes three embossed, fabric-bound, hardcover books, the aforementioned audio, DVD and Blu-ray discs, and four vinyl albums. The latter configuration is limited to 2,500 copies that are numbered and personally signed by Reznor. (At press time, the ultra-deluxe limited edition package had already sold out.)

All paid versions of the collection include immediate access to download all of the tracks.

"More volumes of Ghosts are likely to appear in the future," Reznor wrote on NIN's website.