Johann Sebastian Bach's last name means "brook" in German. That's fitting as the Bach Choir of Pittsburgh started as a small stream of one composer and has traveled to a larger pool during its 75-year journey.

When organist J. Julius Baird founded the Bach Festival Choir of Pittsburgh in 1934, it only sang Bach.

"The Choir was organized by a group of serious-minded people of the North Boroughs," reads publicity from the first season. "They are from all walks of life -- educators, bank presidents, lawyers, manufacturers, politicians, club women and university students." The hope was that Baird would "bring them national recognition and by so doing establish Pittsburgh as a center for the music of Johann Sebastian Bach."

The inaugural concert took place on Dec. 13, 1934, at the North Side Library's Carnegie Music Hall. It's the hall that has been refurbished as the New Hazlett Theater, where the Choir will return this season for its concerts to honor its past.

That first concert was all Bach cantatas and the second was the composer's "St. John Passion." But it wasn't long -- 1937 to be exact -- before the choir decided it needed to look to other composers. That's when it changed its name to the Bach Choir of Pittsburgh.

Some of the highlights of those days include the Choir's only performance with the Pittsburgh Symphony Orchestra in 1950, conducted by none other than Leonard Bernstein. He led the combined ensembles in the Bach's Cantata No. 4, "Christ Lag in Todesbanden" at the now-razed Syria Mosque. After 20 years of directing, director Baird retired in 1954, succeeded by Donald G. Wilkins.

In 1971, the Bach Choir, led by Stanley E. Tagg, joined with the Pittsburgh Opera Chorus for the first opera production (Verdi's "Aida") in the newly opened Heinz Hall. In 1991 the Choir performed Handel's "Messiah" with period instruments.

The group's repertoire began to expand further under director Brady Allred. In addition to choral standards, such as Mendelssohn's "Elijah" and Faure's "Requiem," he commissioned works by the diverse likes of Mack Wilberg, Glenn Rudolph, William Averitt and Dilorom Saidaminova, and performed contemporary classics by Eric Whitacre and David Fanshawe ("African Sanctus").

But the Choir reached its greatest level of diversity with the arrival of Thomas Wesley Douglas. He was hired on an interim basis in the 2004-05 season and hired full time the next season.

"When I came on board, the committee said they wanted to go in a different direction and they knew I had a theatrical bent and wanted to go there," he says. "I like to stay open to new ideas and it reflects that people want to try new things and things that are different. More than going to hear a group stand and sing."

And what a difference. Under Douglas, the choir has commissioned jazz-themed works, sung Bernstein's controversial "Mass" and done two unconventional "Messiahs" -- a space-themed "Messiah," complete with projections and a soprano ascending a ladder to sing, and one among the military vehicles in the Hunt Armory in Shadyside. Each of his six seasons had at least one premiere.

True to form, Douglas has come up with something completely different to open the 75th anniversary season: creating a choral version of Mussorgsky's famous "Pictures at an Exhibition." The concept was suggested by the theme of the different arts influence on music, painting, poetry and dancing, but Douglas got excited about the work.

"I listened to the Mussorgsky all summer, thinking how can I make a vocal arrangement for choir, piano and two percussionists. I just started writing vocal lines for the choirs and a few soloists." The text is "real Latin words, but when you put them together they make no sense. I just put words together that sounded good together.."

Like vocal versions of Barber's "Adagio for Strings," Douglas' "Pictures" will be instrumental in nature and difficult. "It is a real stretch for the singers, exploring the outer reaches of their range."

But the real stretch is the artistic one for the audience, and Douglas believes this is essential to the Choir's relevance.

"I want to see the Bach Choir keep the name Bach but not be limited to one thing. Bach was ahead of his time, and we should be on the edge and doing progressive things."

Like in addition to the singing, five local painters will paint reactions to the performances on the balconies of the New Hazlett.

How would Baird and those founding Bach enthusiast react to this?

"I can't expect that the founders of this would expect the Choir would be the same," Douglas says. "The fact that we are thriving is a testament to the notion of how to we embrace change and stay vibrant."

The rough economy caused the Choir to change one of its concerts this season to a workshop, but Douglas sees that as a temporary bump on this new road.

"Here we are still doing our thing and feeling we are an important artistic force in Pittsburgh," he says. "We are taking it in a different direction, trying to find a niche."

Critics Andrew Druckenbrod and Scott Mervis talk about music on "The Beat," available exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.