Nonesuch released a/rhythmia, the new album from Alarm Will Sound—the 20-member group described by the New York Times as “one of the most vital and original ensembles on the American music scene”—on September 15, 2009.

For a/rhythmia, this new-music band—led by Artistic Director Alan Pierson—performs 14 pieces from composers spanning six centuries, all of which explore the concept of “arrhythmia”: “want of rhythm or regularity, specifically of the pulse.” The resulting work, on the ensemble’s fifth record and its first complete album on Nonesuch, upends order and expectation, often taking ideas akin to minimalism and refracting them through a fun-house mirror.

Central to the disc is the player piano work by Conlon Nancarrow, who has intrigued composers like György Ligeti (also represented on a/rhythmia) and John Adams. Although Nancarrow’s studies were originally thought to be playable only by machines, Alarm Will Sound (along with other intrepid musicians) has, as Pierson writes in his program notes, “set about proving that (at least some of) his studies are actually playable by people.” Pierson calls the final track of a/rhythmia, Nancarrow’s Player Piano Study 3A (his first player piano composition), “the most rhythmically challenging music we’ve ever performed.”

Also on the album are short pieces from English composer-filmmaker Benedict Mason’s Animals and the Origins of Dance and longer works by such artists as Michael Gordon, electronic-music duo Autechre, and the 15th-century composer Josquin des Prez.

After Alarm Will Sound performed the a/rhythmia program in a Carnegie Hall concert last year, the New York Times said that the group “shows an admirable commitment and a spirit of adventure.” New York magazine, in its Year in Culture survey, cited the concert as one of the Top Ten Classical Events of 2008