An exasperated David Perry told his audience at the Barns of Wolf Trap last night "that the humidity was playing tricks on both my guitar and sinuses." Despite his troubles, the virtuoso showman picked himself up beautifully in a program that included both vocal and guitar works by Bach, Sor and Schubert.

Perry ran into trouble after intermission, when he opened with three works by Claude Debussy. The dreamy, impressionistic pieces contrasted well with the exuberant Schubert works in the first half of the concert, and the compositions allowed Perry to explore fully the tonal possibilities of the individual strings. But his concentration crumbled, and two false starts later, the visibly upset Perry apologized. "You know it has to happen at least once," he said, drawing waves of applause from the nearly full house.

For his ending, Perry played five bagatelles by William Walton. This work allowed him to demonstrate his quicksilver fingering. He strained and sweated throughout the virtuoso composition, producing the most exquisite timbres by slapping the strings and picking the bridge.

In the first half, Perry closed with seven of the 20 songs from Franz Schubert's whimsical "Die Scho ne Mu llerin" publicly performed for the first time in his arrangement for eight-string guitar. Although his voice is not rich, it is controlled, and his enunciation is distinct.