L'Arpeggiata's Period Instruments at Zankel Hall "L'Arpeggiata": The ensemble played at Zankel Hall with Gianluigi Trovesi on clarinet, the dancer Anna Dego and the vocalist Lucilla Galeazzi. As it turns out, the alt-classical movement that has become an explosive force in new music also has an early-music wing. And L'Arpeggiata, the flexible period-instrument ensemble that played the first of four programs in its Carnegie Hall Perspectives series at Zankel Hall on Wednesday evening, is determined to be this new division's house band. Just as the composers and ensembles that ply the indie path in new music combine structures and language from contemporary classical styles with gestures and timbres from pop and world music, L'Arpeggiata has lately been hopping through cultures and across centuries. The group uses modern pop vocal inflections and improvisational techniques from jazz in its performances of antique pieces, and it applies Baroque timbres to modern popular tunes. Its audacious hybrids are driven principally by a fascination with reviving the Baroque art of ornamental extemporization and a curiosity about how contemporary improvisatory styles might be enlisted in that quest. Its most recent recording, "Los Pajaros Perdidos" (Virgin Classics), explores the nexus between Spanish and Latin American folk music and pop and elements of Baroque style. There is not much early music on it, apart from a freewheeling take on a Soler Fandango. But the traditional songs have roots in Spanish dance forms, and as you listen to the disc, it can be hard to say definitively, at any point, whether you are hearing Latin pop or a Baroque performance. Songs from the album made up the core of L'Arpeggiata's lively opening program, and most of the time the group's experimental cross-fertilizations worked better live than on the disc. One reason is that the ensemble, led by the Austrian lutenist Christina Pluhar, seems thoroughly at home in the full range of music at hand and thrives on improvisational flourishes. It's one thing for a cornetto player to turn up the heat in, say, Monteverdi, but L'Arpeggiata's Doron Sherwin turned out inventive, shapely solos in pop tunes like Luis Mariano Rivera's wildly rhythmic "Cocoroba" and in the group's sultry arrangement of Consuelo Velázquez's "Bésame Mucho," a highlight of "Los Pajaros Perdidos," offered here as the final encore. For that matter, you don't often hear a Latin torch song like Maria Elena Walsh's "Como la Cigarra" performed with the prominent harpsichord texture that Haru Kitamika brought to it. And Margit Übellacker's psaltery and Lincoln Almada's harp enlivened several pieces, as did David Mayoral's light, tactile percussion. And Bruno Schmidt took a few subtle star turns on a very non-Baroque double bass. Still, the most striking contributions were those of the ensemble's vocalists - Lucilla Galeazzi, who also wrote several of the pieces; the dusky mezzo-soprano Luciana Mancini; Raquel Andueza, a vibrant soprano; and Vincenzo Capezzuto, essentially an alto, though with a timbre and expressive style closer to those of a soul singer than those of a Baroque countertenor. Individually, all the singers were captivating; in ensembles their interactions were terrific, and they were enlivened further when Gianluigi Trovesi, the clarinetist, wove improvisations around the vocal melodies. And a few pieces were enlivened by the energetic theatrical choreography of the ensemble's dancer, Anna Dego. L'Arpeggiata's series runs through Saturday at Zankel Hall and Weill Recital Hall; (212) 247-7800, carnegiehall.org.