The Swiss composer Stephan Thelen wrote the string quartet Circular Lines for the Kronos Quartet’s project ‘50 for the Future: The Kronos Learning Repertoire’. With an eye on its legacy, the Kronos Quartet commissioned 50 pieces that would at once showcase its diverse stylistic range and establish a reservoir of works on which younger quartets could hone their craft. Circular Lines, the programme note of which draws attention to the recent refugee crisis, is combined here with three other string quartets, the latter performed by the Polish all-female Al Pari Quartet.

David Harrington called Circular Lines the most rhythmically challenging piece in the Kronos repertoire – no mean claim. That is due not to the neo-modal material – it’s familiar post-minimalist fare, scalar cells repeating around a key centre – but to the way in which the four voices leap in and out of different metres. The polyrhythmic interplay is the real focus here, and if the harmonic language at times feels uninspired, there is ebullience in the rhythmic entanglement and untangling of the four string voices. The combination of propulsive metre, relentlessly continuous form and call-and-response antiphony is perhaps best appreciated live, but the Kronos Quartet nonetheless give a typically stirring and seamless performance on this album.

In World Dialogue and Silesia, Thelen deploys additive rhythms, polyrhythms, canonic and circle-of-fifths devices to weave a tight post-minimalist web. Everything is honed with intelligence and care; textural contrasts and contrasts of mood come precisely when they should and the unshowy technical craft is likeable. In the middle of World Dialogue, a lyrical section breaks out based on what sound like folk melodies; one feels the Polish quartet, who play throughout with pathos and panache, might have felt at home in this Swiss composer’s Eastern European-sounding music.