Barbara Kolb, one of the busiest and most versatile composers in America, unveiled a modest, graceful tribute to Johann Sebastian Bach last night at the National Academy of Sciences. Opening the sixth season of free concerts by National Musical Arts, Kolb's "Time . . . and Again" is built on a complex set of interactions: between old music and new; live musicians (oboe and string quartet) and a computer-generated sound track; Kolb's music, Bach's and that of electronic composer Craig Harris, who devised the sound track.

In spite of all these complexities, and a structure that features what the composer calls "dissolutions," the new work, commissioned by National Musical Arts, had a smooth, integrated effect in its first performance. The human players interacted well with both the written notes and the sounds emerging from loudspeakers on the stage. The result was hardly simple music, but in the hands of the skilled Washington ensemble it was simply enjoyable.

It needed to be, because it shared the program with Schubert's brilliant, warm and playful Octet in F -- an instantly beguiling composition that bubbles with simple melodies and ingenious structures, wrapped in velvet-smooth sound. Schubert's balancing of three winds with five strings -- a double bass giving fine solidity to the low notes and a horn adding a brassy edge to the softer clarinet and bassoon -- produces one of the most pleasant sounds in chamber music. The sound's texture can be varied from moment to moment to encompass an unlimited variety of moods, and one wonders why this combination is not used more often. Perhaps it is because this combination of instruments is not always readily available; more likely because later composers would rather avoid comparison with Schubert.

Such a comparison is inevitable when a new work has its premiere on the same program with the octet, and it is not surprising that "Time . . . and Again," even with help from Bach, comes in second-best. What is surprising is that it (or any other contemporary work) could stand up so well. Part of the reason may be that (in tune with heartening current trends) the music is not afraid, at times, to be just plain pretty.

Such was not the good fortune of Karl Philipp Emanuel Bach's Quartet in D Major for piano and strings, which opened the program. Even before the audience heard the ingenuities of Kolb and Schubert, it sounded rather square-cut and prosaic, though the slow movement had moments of lyric elegance and there were passing touches of drama in the opening allegretto. The performance sounded adequate but undistinguished -- as though this was the work shortchanged in rehearsal -- but there seemed little in the music to inspire prolonged exploration.