A concert debuting four brand-new compositions comes only once in a long while; that such a concert should take place in Orchestra Hall is almost unprecedented. The Civic Orchestra–and not its parent, the Chicago Symphony–is the audacious presenter here, in cooperation with the American Society of Composers, Authors, and Publishers Foundation, and the quartet of composers showcased are among the best and brightest of the under-35 generation, all possessors of impressive academic credentials. Augusta Read Thomas, represented by Fanfare (commissioned for the American Symphony Orchestra League), is a Northwestern University graduate and now a member of the ultraexclusive Society of Junior Fellows at Harvard; she’s also extremely prolific and works in several genres. David Crumb, son of the old-vanguard composer George Crumb, studied with Lukas Foss and is currently a PhD candidate at the University of Pennsylvania; the ten-minute-long Clarino is his first composition for orchestra. Edward Knight, who also got his PhD from Texas, weighs in with Big Shoulders, a ten-minute celebration of a well-known midwestern metropolis. The concert, under the direction of CSO’s assistant conductor, Michael Morgan, is part of the American Symphony Orchestra League’s national conference in town this week. Admission is free; call ahead for tickets. Wednesday, 5 PM, Orchestra Hall, 220 S. Michigan; 435-8122.