Puerto Rico's contributions to Cuban music (not to mention Spanish-language rap and rock) have often overshadowed the indigenous rhythms of the island. But throughout the history of modern Puerto Rican music, genius musicians have turned their expansive visions to the bomba and plena. These related forms, developed on the northern and southern coasts, respectively, follow a 2/4 time that's similar to merengue, on whose rhythmic foundation bandleaders such as Rafael Cortijo and Mon Rivera built a sophisticated dance music in the '50s. Those are just two of the musicians that Gary Nuñez's Plena Libre celebrate on ¡Estamos Gozando!. Plena Libre have picked up the torch once carried by Cortijo, who sought to make his country's music into mainstream pop. The sound of Gozando is reminiscent of tight, contemporary salsa -- unlike their countrymen Truco y Zaperoko, Plena Libre have less interest in jazzy exploration. Which doesn't mean that Gozando lacks for virtuosity. The trick ending of "Juan José," for example, is dynamic enough to inspire a double take. But the pumping, trombone-led band is best at raising a spirited party vibe, with big, multi-voiced harmony choruses and driving beats pounded out on the music's typical frame drums. The song selection presents something of a Plena greatest hits, including a medley of Cortijo numbers, songs by Mon Rivera, Cesar Concepción and Canario, all deities in the music's history. For traditional Puerto Rican music given a contemporary swing, Plena Libre is matchless. Mark Schwartz