South Korean music is on something of a roll. From popular boy bands such as Super Junior to the array of improvisational acts at this year’s forthcoming K-Music festival in London, there’s a newfound confidence in play. Black String are a quartet named after the Asian zither, the silk-stringed geomungo, with percussion, flute, guitar and electronica also in a mix that swings comfortably between east and west, Korean folk and jazz. This second album alternates contemplative numbers such as the minimalist title track with pieces of shamanic abandon like Exhale-Puri, with its crashing drums and fevered vocals. You can never be certain what’s coming next. The opening Sureña is an impressionist South American travelogue, Hanging Gardens of Babylon is nine frenzied minutes led by an oud-like horn, while Radiohead’s Exit Music is given a slow (and non-vocal) treatment. Vietnamese-French guitarist Nguyên Lê adds jazzy discordance to two numbers, including Song of the Sea, an otherwise straight, albeit muscular piece of folk. There are tricky time signatures, a nod of thanks to Ornette Coleman’s Lonely Woman for a guitar solo, and constant tonal shifts from the geomungo itself. Elegant and accomplished.