As Pwyll ap Siôn noted in his 80th-birthday feature on the composer (A/15), there is more to Terry Riley than In C, which has proved both the basis of his fortunes and a millstone for his reputation. Those familiar with that masterpiece of minimalism, or the improvisatory works of the 1970s, may well be surprised by the more precisely notated and through-composed works on this new release, played by the pioneering Del Sol Quartet.

Dark Queen Mantra (2015), for string quartet and electric guitar, was composed ahead of Riley’s 80th birthday for the Del Sol to perform with his son, Gyan. Its three movements were inspired by Spain: a hotel, a Goya painting and – more elusively – the ‘dark queen mantra’ of the complex, large-scale finale in which, as Riley comments, ‘it gets dark’. The rapport between quartet and guitarist is palpable in a performance that compels attention, so much so that one can forgive the occasional intonational indelicacies. These are absent from The Wheel & Mythic Birds Waltz (1983), a multifaceted fantasy for quartet on jazz and Indian rhythms that never involves a waltz – although allegedly Tibetan birds had a hand in its inspiration!

Set between them are the five reworkings or reimaginings of Monteverdi madrigals that comprise Mas lugares (2003) by virtuoso double bassist and composer (and occasional collaborator with Riley) Stefano Scodanibbio (1956-2012). An object lesson in how to create fully satisfying music expressively and technically, Mas lugares is a real find, the centrepiece of a splendid, if challenging, disc.