Since forming in Copenhagen in 2002, this string quartet has achieved respect and popularity by balancing rigorous craftsmanship and airy ambience with the hip persona evoked by members' shaggy beards. The group made its mark with a survey of quartets by Danish modernist Carl Nielsen, conveying his swings from playful to brooding with unstudied elegance. The ensemble's repertoire includes essential work from the likes of Beethoven, Bach and Brahms; 20th-century music by compatriots like Hans Abrahamsen and Per Nørgård; and adaptations of Scandinavian folk tunes, all interpreted with equal parts precision and panache.