It’s often said that the distilled essence of composers can be heard in their string quartets. And so it is with Glass, whose quartets here show a craftsman of considerable invention. String Quartet No. 6 begins as a bustling burst of dense energy, its second movement beautifully meandering, rich, and complex. The single-movement String Quartet No. 7 is almost Beethovenian in its restless questioning. Arranged for string quartet (with two violas), the Saxophone Quartet is warmly scored and yet shows Glass at his most forensic, with each bar stunningly sculpted.