So rich and varied is the Choral Arts Society's contribution to the Philadelphia community that you couldn't help but want its 30th-anniversary concert, held late Sunday afternoon at First Baptist Church, to put a better foot forward.

Starting the program with Bach's Magnificat, as great as it is, certainly didn't do that, and perhaps could not be expected to. Most performances I've heard (and especially ones that I've sung) were highly approximate - which was the accepted price of hearing this intricate, five-part choral writing until smaller, more accurate groups raised the prevailing performance standard. The Choral Arts performance was "old school" in that sense, and had bad luck as well.

From the opening orchestral tutti (in which the original-instrument players seemed to have trouble hearing one another in the church acoustic), the piece's challenges were as audible as its greatness. Artistic director Matthew Glandorf had the enterprising idea to use the so-called Christmas interpolations Bach wrote for an earlier version of Magnificat that made it more seasonal.

However, the performers' lack of familiarity didn't put this music in the most flattering light. The only section that went well was the duet, "Virga Jesse floruit," with soprano Justine Aronson and bass Ryan Tibbetts, the latter an interesting casting for Bach with his lighter, baritone timbre. Tenor Steve Bradshaw was also a pleasure to hear.

Bach was followed by the Vivaldi Gloria (RV 589, the best known of the composer's settings) and Mozart's Ave Verum Corpus that presented the Choral Arts Society that we know and love - with a warm, full-bodied tone quality that also revealed the inner workings of the harmonies where the music's narrative is heard.

As in the Bach, alto Jenifer L. Smith was a vocally distinctive presence in the Vivaldi. From my seat in the church's loft, my view of the soloists was sometimes obscured, so that when one of the soprano solos had such radiant tone and knowing style, I wondered, "Who is that?" Answer: local freelancer Leslie Johnson, whom I've heard often and who always delivers such artistic surprises.