Puerto Rican bassist and bandleader Gary Nunez formed Plena Libre a decade ago to revive and preserve his island’s plena tradition. The form emerged toward the end of the 19th century when the music of immigrants from nearby Barbados began mixing with Puerto Rico’s own African-derived musical forms, sounds akin to those developing across the water in Cuba. In its earliest incarnations plena was a narrative style that often functioned as a record of the times, putting the latest political and cultural happenings into verse. Its sound was defined by pandeiros, tambourinelike hand drums, and the scraped gourd called the guiro, both used to sculpt elaborate polyrhythms. For most of the 20th century plena was at the core of Puerto Rican music, but by the 70s pan-Caribbean salsa and merengue increasingly relegated it to the back of the drawer; still, with its galloping grooves and use of the clave, plena isn’t far removed from these styles. After making nine albums with original tunes, on the new !Estamos gozando! (Times Square) Plena Libre pays homage to some of plena’s great past practitioners–Angel Torruellas, Los Pleneros de Quinto Olivo, Mon Rivera, Rafael Cepeda, and others. Yet the material’s arranged sleekly, with glossy, radio-friendly vocal harmonies and an ear toward contemporary dancers. Nunez is touring with a seven-member version of the band (it’s frequently featured twelve), which ought to ensure that the emphasis stays on the beat. Dance lessons precede the performance at 6 PM. Free. Thursday, July 15, 7:30 PM, Spirit of Music Garden, Grant Park, Michigan between Harrison and Balbo; 312-742-4007. Plena Libre also makes a free appearance Wednesday, July 14, at 5 PM at the Virgin Megastore at 540 N. Michigan; 312-645-9300.