Sooner or later all aspiring composers have to come to terms with J.S. Bach: with his formal rigor and his masterful use of theory to serve emotion, he casts a long shadow. The Art of Fugue, his exhaustive study of counterpoint, sometimes seems as much a hermetic meditation on self-imposed limits (the entire work consists of fugues and canons on a single theme) as a piece of art meant to engage a listener. Nonetheless, it's representative of Bach's output, summarizing his contrapuntal and harmonic ideas in a final testament; he worked on it throughout his last decade, and it was published, still unfinished, shortly after he died in 1750. In 2002, to celebrate their first decade, the Brentano String Quartet commissioned ten composers to write companion pieces to selected contrapuncti from this work; they'll perform them here as part of the "University of Chicago Presents" series, pairing each with its inspiration. The range of composers is broad: they include Wynton Marsalis, serialist Charles Wuorinen, electric guitarist Steven Mackey, and Chou Wen-chung, an 80-year-old disciple of Varese. Sofia Gubaidulina has filled Reflections on the Theme B-A-C-H with tormented musical allusions that coalesce and then quickly shatter, as if reflection itself were too painful to engage in for long. As its title implies, U. of C. professor Shulamit Ran's Bach-Shards employs a similar (if less anguished) approach, with fragments of the theme thrown dazzlingly and dizzily around the ensemble. It's also one of the strongest pieces, capturing Ran's voice yet clearly arising out of Bach's. For their part, the Brentano players (Mark Steinberg and Serena Canin, violin; Misha Amory, viola; Nina Lee, cello) glide over some of Bach's dissonances so blithely that he sounds like the most even-keeled composer on the program. Friday, January 23, 8 PM, Mandel Hall, University of Chicago, 1131 E. 57th; 773-702-8068. At 7 PM there will be a preconcert discussion with violinist Steinberg and Michael Kannen, the Sidney Friedberg Chair in Chamber Music at the Peabody Institute and a founding member of the quartet.