There was a critical difference on Wednesday at Ambassador Auditorium when the Los Angeles Chamber Orchestra made its seasonal presentation of the six "Brandenburg" Concertos of J. S. Bach at a single sitting: the presence of conductor Nicholas McGegan, guiding spirit of the San Francisco-based Philharmonia Baroque Orchestra, and quite likely this country's foremost purveyor of 18th-Century performance style.
McGegan drew from his local charges the bouncy rhythmicality and a suggestion of the lean, keen-edged tone that characterizes his period-instrument orchestra.
Still, this was not an occasion for savoring ensemble values. Maintaining perfect unanimity at the blistering tempos chosen by McGegan for portions of the First, Second and Fourth concertos proved beyond the ability even of players as accomplished as those of the LACO.
Thus, the concert served to highlight strong individual contributions: the controlled fire of Patricia Mabee's harpsichord cadenza in No. 5; the expressive trio of oboes led by Allan Vogel in the adagio of No. 1 (hectic pacing ruled against the horns' and oboes' ability to do more than valiantly stay in the game during the fast portions); the lively David Shostac-Susan Greenberg transverse flute duo (in place of recorders) in No. 4 .