The Left Bank Quartet brings its unique vision to three pieces connected by the number six: Beethoven’s Sixth Quartet, Webern’s Six Bagatelles and Bartok’s Sixth Quartet. And with the final La Malincolia movement of the Beethoven; the recurring elegiac “Mesto” of the Bartók; and Webern’s stark musical sketches that convey life’s uncertainty, the notion of melancholy—and our sometimes triumph over it—is the other common denominator.