Consider the viola. The violin's larger and lower-voiced cousin could be characterized as the unsung hero of an orchestra.

It's the instrument responsible for the hardy, husky, muscular sound at the center of the string section, a role so central that many of the great composers gained much of their orchestral education while sitting in the viola section. Mozart, Haydn, Beethoven, Dvorak: Violists all.

Yet, when it comes to booking soloists to appear with major orchestras, seldom is there a violist among them. One of the lone exceptions is Germany's Tabea Zimmermann, who might just be the world's most widely respected violist.

And, as of this weekend, she's the newest St. Paul Chamber Orchestra artistic partner. That means she'll be coming to town two or three times a season for the next few years, performing the music of her choosing with members of the orchestra.

Her tenure began Friday at Eden Prairie's Wooddale Church with two concerts featuring works of Ödön Partos, Béla Bartók and Johannes Brahms. And the evening performance proved a very satisfying sonic journey, an expertly interpreted combination of mournful modernism and brightly colored Brahms.

Zimmermann might represent a "get" akin to securing superstar violinist Joshua Bell as one of the original SPCO artistic partners in 2004. Her status among violists is fairly comparable, when you subtract the extra pop culture attention accorded violinists. Zimmermann is what you'd call a musician's musician.

That was clear from the evening's first work, Partos' "Yiskor (In Memoriam)." Partos was a Hungarian violinist who landed in Palestine shortly before World War II and became the Israel Philharmonic's principal violist for 18 years. In 1947, he composed "Yiskor" as a means of honoring victims of the Holocaust, and Friday's performance left me asking why I've never heard this powerful piece performed in a Twin Cities concert.

For anyone dealing with the loss of someone dear to them (and I'm among them), "Yiskor" may prove the ideal musical expression of grief. Unlike the ethereal violin, the viola has a grounded sound more in line with the range of a human voice. And Zimmermann filled the expansive church with an urgent evocation of the pain of separation, the SPCO's strings offering layers of comfort akin to the words of an empathetic friend.

Written by another Hungarian of the same era, Bartók's Divertimento for String Orchestra bore a dancing tone, at least in its outer movements. But the slow central movement took things in a far darker direction. One could hear that this was composed on the eve of World War II, for it's full of fear and anxiety. Zimmermann and the strings made it gripping, hypnotic and ultimately explosive.

After all that sorrow, Brahms' Serenade No. 2 could have seemed incongruously light, but perhaps Zimmermann and the SPCO concluded that some dessert was in order. The addition of winds offered some welcome warmth and a refreshing variety of voices. Flutes fluttered, French horns bellowed jollily, and delightful solos rang out throughout the orchestra. It seemed something of a party, appropriate for a celebration of this promising new partnership.

Zimmermann will spend a second weekend with the orchestra on March 16-19, joining them for music of Johann Hummel and Fanny and Felix Mendelssohn in Northfield, St. Paul and Arden Hills.

St. Paul Chamber Orchestra

With: Violist Tabea Zimmermann

What: Works by Ödön Partos, Béla Bartók and Johannes Brahms

When: 8 p.m. Sat., 2 p.m. Sun.

Where: Ordway Concert Hall, 345 Washington St., St. Paul

Tickets: Free-$50, available at 651-291-1144 or thespco.org

Rob Hubbard is a Twin Cities classical music writer. Reach him at wordhub@yahoo.com.