The musical life of our times is happily blessed with an abundance of young new string quartets. That makes it all the more instructive to go back to an older quartet always hailed as a pioneer of the highest modern standards and go beyond its studio recordings to the quartet’s heyday and the “acid test” of a concert (1965). And that conforms to the maxim of the Juilliard String Quartet that new music should sound classical and old music should sound like new, not only with Dvorák and Mozart but even with Bartók.