For his fourth solo album, now in Spatial Audio, Icelandic composer Ólafur Arnalds mixes synths with acoustic strings and piano. Its title track showcases pioneering new Stratus software that controls two self-playing, semi-generative player pianos. It’s a dreamlike soundworld that Arnalds juxtaposes with racing minimalist rhythms and pulsing electronic beats. The now-familiar use by post-classical artists of a muffled, close-miked upright piano has never sounded so sweet as it does in “saman,” while hypnotic, fluid textures of “they sink” envelop the velvet sound of a solo cello. Electronica provides the beating heart for the gently oscillating “ypsilon” before the final “nyepi,” one of Arnalds’ most introspective, affecting soundscapes.