AFTER HEARING the Kronos Quartet perform "Purple Haze," you might have found yourself asking, "What next? The Turtle Island String Quartet doing 'Crossroads'?"

Well, as it happens, yes. The Robert Johnson delta blues classic adds an unlikely but not entirely unexpected coda to the band's latest album, "Skylife." In the past the group has recorded other familiar material -- a rather stilted version of "A Night in Tunisia" comes to mind -- but this time around the band's chamber group instrumentation contributes considerable tension and drama to Johnson's haunting tale.

The rest of the album is typically ambitious, and the musicianship displayed by violinists David Balakrishnan and Darol Anger, violist Katrina Wreede and cellist Mark Summer is first-rate. Together they project a vibrant ensemble sound distinguished by alternately astringent and lush harmonies and colorful percussive effects. Individually, they play with great precision and increasingly seem more attuned to jazz.

While swing tunes along the lines of "Blues for Oaktown" are apt to be the first to appeal to the uninitiated, far more so than than the jagged contours and dissonant harmonies found on "Dexteriors" or "Mr. Twitty's Chair," overall the album's greatest strength lies not in any one performance or style but in its constantly shifting moods and textures.

THE TURTLE ISLAND STRING QUARTET -- "Skylife" (Windham Hill). Appearing Saturday at the Barns of Wolf Trap.