Herr Lachenmann is a cruel taskmaster. If these intimidating words of his were to lead to something as tangible as the Berio Sequenza, or Beethoven's Grosse Fuge — which began the Arditti's program with its challenge delivered out of a cannon's mouth, so "liberating" that we still cannot fully grasp the extent of the space it demands — I might react with greater pleasure to his demands. (I might, in other words, know what the hell he's talking about.) But his Quartet turned out to be more empty space sporadically poked through by notes. Morton Feldman's music is a little like this sometimes, but I find the four hours of Feldman's For Philip Guston a marvel of concision up against Lachenmann's half-hour near-silent scream.