There are always debates about how to effectively measure a youngster's musical talent.

Mary Persin's family simply used a ruler.

"My first violin was a ruler with a cereal box in the shape of the violin so I could learn how to hold it," Persin says with a tinge of embarrassment in her voice. She was only 21/2 at the time, a tagalong on her older sister's violin lessons in their home of Greensburg. Persin wanted a real violin like her sister's in the worst way, but her parents felt it wasn't quite time. "Even if the 1/16th violin is only $100, you don't want the kid to drop it."

Soon enough, however, Persin got the real deal and soared with it. Later she switched to viola and is now a member of one of the brightest young quartets in the nation, the Biava Quartet, which will perform new works, including a new quartet by David Stock, on a special Pittsburgh Chamber Music Society series this spring at the New Hazlett Theater. It's the quartet's first appearance in Pittsburgh.

The Biava Quartet formed in 1998 at the Cleveland Music Institute. Some of the members were freshmen and others, such as Persin, were still in high school. They are now assistants to the Juilliard Quartet at the Juilliard School in New York.

"It is highly unusual that a quartet would start so young and stay together," says Persin, although the quartet did replace two members early on. It is now violinists Jason Calloway, 27, and Hyunsu Ko, 29, Persin, 28, and cellist Austin Hartman, 29. Among their many trophies is a Naumburg Chamber Music Award, and the quartet has performed at Carnegie Hall, the Kennedy Center, Wigmore Hall, Alice Tully Hall, the Aspen Music Festival and more.

All renowned venues, to be sure, but Persin is just as excited to make a return to Western Pa., where she played in the Pittsburgh Youth Symphony Orchestra and the Westmoreland Youth Symphony (and was valedictorian of Hempfield Area High School to boot).

"It was an ideal suburban upbringing: a good school and some acres to run around with, but we were able to go to the city a lot," she says.

Persin's family was musical, but she exceeded all expectations.

"I never had parents that forced me," she said. "It was always something I wanted to do. It was my love and my passion."

There's the time, in 1991, that Persin auditioned for Chautauqua Institute at 11 years old -- two years earlier than students are allowed because they live in dorms. Predictably, she won the audition. At first, the summer program denied her access, but finding out that her family would be summering there, it acquiesced -- but only if Persin would switch to viola to help it fill a gap in its youth orchestra.

"I ended up playing in a quartet with some kids who were going to Curtis [Institute of Music]," she says.

Clearly Persin was destined to be a professional musician.

In Pittsburgh, she studied with Hong-Guang Jia and Stephanie Tretick, and at 16 she started to commute to Cleveland to study with the principal violist of the Cleveland Orchestra, Robert Vernon.

Now she and the members of the Biava Quartet, named after conductor Luis Biava, perform about 100 concerts a year, in addition to many other educational duties such as when it becomes quartet-in-residence at the Brevard Music Festival this summer. Because Persin's husband, PSO's resident conductor Daniel Meyer, runs orchestras in Asheville, N.C., and Erie, the couple hasn't seen much of each other since being married in August of 2007. "We haven't come near 365 days together yet."

Persin racked up many more days than that in Pittsburgh. "I have so many memories of going to Carnegie Music Hall to hear so many great quartets. It is really an honor to be playing on the same series."