PERFORMING ARTS

Turtle Island Quartet, Sergio and Odair Assad

The title of Saturday night's program at the George Mason Center for the Arts was "String Theory," but it wasn't a lecture for the astrophysicist set. The theory in question was whether classical musicians can throw off their chains and play anything from jazz to world music. There to test the case were two of the most formidable crossover groups on the planet -- the Turtle Island Quartet (which just won a Grammy for its take on the music of John Coltrane) and the brilliant guitar duo of Sergio and Odair Assad, whose repertoire ranges from Couperin to Gershwin to Antonio Carlos Jobim.

It was a mighty teaming, and in a virtuosic program that started with bop and ended in New Age pastiche (with stops along the way for '70s fusion, 20th-century classical and Argentine tango), there were moments of real and striking beauty. In particular, the Assad brothers (so gifted they could make Bulgarian drinking songs sound good) turned in achingly nuanced accounts of Isaac Albéniz's "Cordoba" and their own highly personal "Tahhiyya Li Ossoulina."

But for all that, it was a rather tame evening. It's not easy to combine the intellectual precision of the classical world with the spontaneity and sensuality of jazz and pop, and the Turtles' take on tunes such as Coltrane's "Moment's Notice" often sounded like pale, bloodless imitations of the real thing. There was more electricity onstage when the Assads joined the quartet for Latin American works including Sergio Assad's "Djembe" and Astor Piazzolla's "Verano Porteno" -- intricate, multi-layered music brought off with elegant grace -- but the evening overall had the feel of an academic exercise: well-played and thoughtful, but without much fire at its core.

-- Stephen Brookes

Collegium Vocale Gent

Belgium's Collegium Vocale Gent opened the Library of Congress's 83rd season of free concerts Friday night. A program devoted to Haydn was an early start on the tributes planned for the 200th anniversary of the Austrian composer's death next year.

Twelve singers, in mixed formation, performed selections from the three- and four-voice German songs (Hob. XXVb and XXVc). The songs were reordered to present a moral lesson, proceeding from an old man confronting the specter of death, through his memories of youth and pleasure, to the most beautiful songs, addressed to God. The group encored the best of those sacred songs, "Abendlied zu Gott," an evening song of thanksgiving for life's gifts, providing an eloquent epitaph for Haydn.

The singing was exemplary, the result of careful attention to intonation, transparent balance of parts and declamation of text. In particular, soprano Roswitha Schmelzl spun a mellifluous melodic line in her solo song "Das Leben ist ein Traum." The audience, which insisted unfortunately on applauding after every number, spoiled the joke at the end of "Die Beredsamkeit," where an unfinished final cadence is supposed to show, ironically, how water makes us quiet.

Guest director Kristian Bezuidenhout added virtuoso flair with keyboard pieces played on an exquisite John Lyon fortepiano, a modern copy of the Anton Walter instrument owned by Mozart. The F Minor Variations (Hob. XVII:6) called to mind Alfred Brendel's performance of that work during his farewell recital last spring. The gentle tone of the fortepiano gave a more wistful color to the wispy roulades, fanciful embellishments and fragile, truly pianissimo minor sections.