In a career that dates back to the '70s, Japanese pianist and composer Ryuichi Sakamoto has crafted pop songs, film scores, and experimental works. Austrian guitarist Christian Fennesz is known for crafting dense soundscapes that can be peppered with glitches while being seductively melodic. They collaborated on the EP Sala Santa Cecilia and the full-length Cendre, and in 2011 they released the double album Flumina, which has an interesting genesis. While on tour in Japan, Sakamoto opened every concert with a different piece, each in a different key. Sakamoto was aware he'd later send recordings of these performances to Fennesz, who'd then add new material. The resulting tracks don’t vary a great deal; they're generally spare, spacious, and full of nuance. (Most of the pieces are consonant, but some, such as “0405,” display a delicate dissonance.) There's enough variation on Flumina to reward close listening; for instance, “0407” has subtly distorted piano tones that are a bit macabre. Little touches like that keep things interesting.