If Beethoven's Fourth Piano Concerto is a dialogue between soloist and orchestra, then his Fifth, the Emperor, is a confrontation. Its bold opening announces a work that, like his Eroica Symphony, is on a grander scale than anything before it--the roar of middle Beethoven at its peak. Pianist Stephen Hough's exceptional touch and control seem best suited to the glorious middle-movement adagio, where he can be expected to suspend time, though his relatively lean and unsentimental way with the Romantic repertoire might not do full justice to the rugged outer movements. Also on the program is Prokofiev's Fifth Symphony, whose rewards lie more on the surface than those of the darker, more brooding works Shostakovich wrote during the same period. This symphony was a favorite of the composer, who saw it as glorifying the human spirit, and it overflows with wonderfully orchestrated melody and shifting moods. The demands it places on any orchestra, particularly the winds, are also considerable, so the members of the Grant Park Orchestra can safely skip this week's trips to the gym. Carlos Kalmar conducts. Sat 8/19, 7:30 PM, Pritzker Pavilion, Millennium Park, 100 N. Michigan, 312-742-7638. Free.