Concertante di Chicago is a recent entry in the growing roster of specialty ensembles that have enriched (and enlivened) our town’s music life over the past few seasons. The name is derived from the Italian verb concertare, meaning “to get together,” and that’s what these musicians do. Playing without a conductor music that is in some sense soloistic, this chamber orchestra’s instrumentalists are all equal partners, taking turns in solo and supporting parts. Another unusual practice: before each performance, the musicians explain to the audience how they think the piece ought to be interpreted. The ambience thus conveyed is one of informality, collegiality, and intense involvement. This season-opener program is an excellent sampler of the concertante genre, ranging from the baroque (Gluck and his contemporary Dittersdorf) to the neoclassical (Stravinsky). Many of the Concertante members are affiliated with DePaul University’s music department. Sunday, 7:30 PM, concert hall, DePaul University, 800 W. Belden; 940-8099 or 853-3636.