"It was my own idea," says Fischer, "and its only goal is a deeper understanding of the work. There are two types of reflections in Bach's Passions: the story told by the Evangelist is interrupted by either an aria or a chorale. The arias are individual, emotional responses, full of passion and often doubts. The chorales are more peaceful; they are the collective responses of the community to the Gospel.

"These Lutheran songs were well-known to the community that filled the church in Bach's time," the conductor continued, referring to the chorale tunes — a number of which, such as "O Haupt voll Blut und Wunden" ("Oh, sacred head now wounded") remain familiar hymns today. "Bach's Passions (or cantatas) were composed for a church service, not a concert hall. And, like in every liturgical service, the community takes part in the singing. Taking part in the singing helps [a modern-day audience] to experience the original meaning of these works."

Nevertheless, such an audience-participation format is unusual in today's concert world, and it may be telling that the "choir seats" were priced at a discount at all three venues: St. George's Church in Bristol, England (tonight); the Concertgebouw in Bruges, Belgium (Saturday, March 31); and the Queen Elizabeth Hall at London's South Bank Centre (next Monday, April 2). Fischer will lead rehearsals for his audience of singers before each concert, though these aren't mandatory.

Was it difficult for Fischer to get the venues and the OAE, now Britain's most prominent period-instrument band, to go along with his idea? "The Orchestra of the Age of Enlightenment is well-known for its experimental spirit," he says. "They were enthusiastic. Some practicalities had to be solved, like the language problem. I chose a dual-language solution: The work will be performed with the original German text, but the chorales will be sung in English in England." (The Flemish being famously adept at foreign languages, the Bruges audience will sing the German chorale texts, though the Concertgebouw is offering a program book with both the original libretto and a specially commissioned Dutch translation, along with musicological commentary.)

Another sort of audience participation will be available on Sunday (April 1), as the South Bank Centre offers one of its well-known Study Days devoted to the St. Matthew Passion. Fischer's two lead soloists for this project, tenor Rufus M‹ller (singing the Evangelist) and baritone Peter Harvey (Christus), will discuss the work and how they approach their roles in a late-morning panel discussion; that afternoon, they'll conduct a master class on the score with young singers and instrumentalists. Information on both the Study Day and the London "People's Passion" is available at www.southbankcentre.co.uk.