Nearly fifty years on, minimalism has become the stuff of cliché, its devices endlessly exploited on film and television soundtracks. Yet Riley and Pärt, who are marking their ninetieth birthdays this year, remain intriguing outliers, notable for the stubbornness with which they have held to their youthful convictions. Riley remains active as a composer and an improviser, collaborating with performers six or seven decades his junior. Pärt, who has apparently retired from creative work, offers an output that is far more complex and contradictory than his monkish public image suggests. Recent celebratory concerts dedicated to the two have been sites not of reverence but of restless rediscovery. Both retain the power to make the familiar strange.