During the 1980s, when period-instrument ensembles were first creating a stir in the United States, intense debates arose as to whether the music of J.S. Bach should be played on modern or period instruments. Early Music advocates argued that the composer wrote his keyboard works for the harpsichord or clavichord, both of which have a very different timbre and dynamic range than today's modern piano, which was only beginning to be developed toward the end of Bach's lifetime.

The modern-instrument camp countered that much of Bach's music has a disembodied quality that is seldom instrument-specific; he was not against stealing from himself so that vocal works often mimicked instrumental writing, violin concertos showed up as piano transcriptions, and grand choruses were reinvented as overtures. Besides, they would add, the piano brings a new breadth to the music that should not be denied Bach simply because he had the fate to be born before the instrument's invention.

Today, style-conscious performers like pianist Peter Serkin and the Brandenburg Ensemble find that Bach can stand up to the sound of modern equipment while benefiting from the stylistic experiments of the Early Music movement, including matters of color, tempos, articulation, and phrasing. This will be demonstrated on November 5 and 9 when Serkin and the ensemble, directed by the violinist Jaime Laredo, appear at Avery Fisher Hall to perform Bach's concertos for keyboard as part of Great Performers' "Chamber Orchestras" series.

"As far as period versus modern instrument playing, I don't really think in those terms," says Serkin, who has performed Bach on both harpsichord and piano. "Even prior to the last 25 years I was always interested in the sonorities of the harpsichord and clavichord. But there's always some question as to what these pieces were written for."

Serkin's personal heritage is as rich as any modern-day musician‹his father was the late, renowned pianist Rudolf Serkin; his grandfather, the violinist and composer Adolph Busch‹and is attuned to recent Bach scholarship. His recordings of the Goldberg Variations, the Inventions, and Sinfonias are celebrated for their rigor and integrity as well as emotional depth. And he is particularly fascinated by evidence that has come to light in Bach biographer and Harvard professor Christoph Wolff's authoritative book, Bach: The Learned Musician, which suggests that the composer had greater knowledge of the early piano than was once believed.

Wolff's book explores the long-established belief that the composer performed his concertos for keyboard on a harpsichord in Zimmerman's coffeehouse in Leipzig during the 1730s with his Collegium Musicum ensemble. Surviving advertisements for these performances stated that the concertos would be played on an instrument, "the likes of which had never been previously heard." This is corroborated by correspondence between Bach and a local instrument dealer that indicated Bach's professed interest in the new fortepiano.

"It really is quite a different story from the orthodox version presented up until now, which suggested Bach wasn't really interested in the piano," says Serkin. "So I'm just wondering if this new instrument‹the likes of which no one had ever heard in Leipzig up until that point‹may have been a precursor to the modern piano. As outlandish as it seems, [Bach's keyboard] might not have been that different from today's."

Beyond the question of old versus new instruments, Serkin has a keen interest in matters of performance style. While he will play on a modern Steinway, the instrument will be positioned, Baroque-style, at the rear of the stage, surrounded by the ensemble's 15 modern strings (a very un-diva-like gesture for any soloist). A supportive harpsichord continuo will also be added to the texture, giving the bass line added rhythmic vitality.

Serkin approaches other stylistic matters with a historically attuned ear. He points out that Bach's keyboard concertos are mostly arrangements of sacred cantatas, and this legacy should be reflected in articulation and phrasing. "The consonants of the words can be mirrored on the keyboard," he says. "In articulation, it's not merely a question of staccato and legato but phonetic pronunciations."

He continues, "That's what's so much fun about playing with the Brandenburg Ensemble and Jaime Laredo. They're very sensitive to that, so much so that one doesn't have to spell it all out in advance. One can actually adjust articulations and phrasing on the spot and they respond to it."

Along with the seven concertos for keyboard, Serkin and the Brandenburg Ensemble will present the Brandenburg Concertos Nos. 3 (G Major) and 5 (D Major). Serkin finds similarities between these concertos and music of the present. "They remind me of some newer music in the sense that everything is interwoven in the entire work. It's not so much a separate, dualistic approach [between soloist and ensemble] as there is in the Romantic concerti."

The Brandenburg Concerto No. 5 also calls on the keyboard soloist to engage in some bravura display in its virtuosic, 65-measure cadenza. Reviewing a recent performance by Serkin, Los Angeles Times critic Mark Swed noted that he "played that extraordinary passage of the Fifth Brandenburg where the piano commandeers the first movement with the kind of alluring virtuosic abandon that would unnerve most historically inhibited Bach players today."

Serkin is matter-of-fact about the concerto's challenges. "In the Brandenburgs, when it comes to a question of playing absolutely alone, the Fifth is very unusual," he says. "I think people had never heard anything like it. The cadenza is extraordinary‹incredibly intense and really thrilling."

Brian Wise, a producer at WNYC radio, writes frequently about classical music.