In less than a year of existence, the Bach Society seems to have pushed completely aside its parent organizations, the Harvard Music Club. However unnecessary the displacement, the reward has been considerable: a student ensemble of increasing finesse devoted to the chamber literature.

Sunday's concert opened with a new work, Victor Yellin's Passacaglia for String Orchestra. Over a repeated bass passage, Yellin has devised an extended development that builds to unusually powerful climaxes; even his use of dissonance seemed subordinate to the overall dramatic pattern. The rhythms had a tendency to excessive four-squareness, at least on first hearing, but sincerity and intense emotion kept the Passacaglia nearly always exciting.

The performance of Bach's Cantata N. 21 relied heavily on sheer volume to make its effect, but did great credit to the leadership of conductor Michael Greenebaum. From an organizational standpoint alone, the cantata is a huge undertaking; Greenebaum succeeded in offering both a well-rehearsed ensemble and a measure of interpretive continuity. He was especially fortunate in soprano soloist Jean Lunn. To her customary refinement of diction and gifted insight into the music as a whole. But her singing and a few instrumental solos were the only high spots. The chorus sang with colorless tone and indifferent diction most of the time. Furthermore, Greenebaum made the texture bottom-heavy with a basso continue of four cellos, double bass, and bassoon. As a result, big ensembles plodded badly and the duet for soprano and bass seemed interminable until it finally expired.

The climax of the evening came in Robert Freeman's reading of the Mozart Piano Concerto N. 22. He imparted all the clarity the score demands, yet never thumped the keys; his runs contained generous coloring, yet were without excessive pianistic mannerisms. Freeman's use of rubato may be circumspect to some, but it certainly never passed the bound of good taste. A particularly delightful detail was his articulation of the finale's main theme. Because of his slight stress on the last note of the motive, its repeated rhythm could never even approach monotony. The orchestra provided superb accompaniment, and their many incidental solos showed a polish to match the pianist's. There could have been few better manifestations of the growing integration that can, in time, produce an outstanding performing organization.