As the owner of a small business in Annapolis, Patti Platt always felt so frazzled and busy that she couldn't imagine taking even one night away to gain a little perspective.

Hers, she says, was a life out of sync — or, more aptly, a life out of tune.

Then she decided to join the Chesapeake Harmony Chorus.

"I used to think there was no way I could make time for something like this," said Platt, 58, as she cheerfully shed her overcoat, did a few vocal warm-up exercises and stepped into a circle of 15 women for a two-hour session of barbershop-style harmonizing Wednesday evening. "Now I can't do without it. It's the night I look forward to most."

It was 7:30 p.m. at Historic Baldwin Hall in Millersville — rehearsal time for Chesapeake Harmony, a small and enthusiastic chapter of Sweet Adelines International, a worldwide organization that has been turning four-part a cappella singing for women into an avenue for social and musical blending since the 1940s.

Nearly 20 women, mostly from Anne Arundel, are members of the chorus, the smallest of three such chapters based in the county.

"I love the musical challenge, and it's such fun to be around [this] group of women," says Leone Craven, 62, an Arnold resident who helped start the chapter in 1998 and has been a member ever since. "And singing has health benefits. They say it releases endorphins in the body. I can't quote you all the science, but you can certainly feel it. Singing is a wonderful way to leave the baggage of the day behind and reduce stress."

For members like Platt and Craven, Chesapeake Harmony offers a chance for female singers of all ages and backgrounds to do what most "barbershop" groups do — divide into four distinct groups based on vocal range (the tenors, leads, baritones and basses), and then, working with musically layered tunes such as the old standards "I'm Looking Over a Four-Leaf Clover" or "God Bless America," weave the parts into a smooth, tightly woven tapestry of sound.

"When it's done right, it sounds great, but it's harder than it looks," says Platt, a baritone.

The group also provides a sort of family-reunion feel that extends a sense of welcome to all female comers, as long as they can carry a basic tune, absorb a few good-natured barbs and commit to attending on a regular basis.

"You can join for any reason," says Constance "Tancey" Bosna, the group's perpetually upbeat director. "You can join because you love to sing, because you love to organize, because you like doing PR, because you want to be a president of something.

"We're each other's best friends. My sisters don't call me as much as they do," adds Bosna, a 32-year member of Sweet Adelines and a veteran director who enjoys Chesapeake Harmony's singing and camaraderie so much that she drives down from her home in Philadelphia to make the weekly rehearsals.

It was an open-house night, the first of four Wednesday evenings during which the club plans to open its doors to any and all comers this month. And if the handful of newbies in attendance were paying attention to such things, they learned there was at least one pair of sisters in the chorus, not to mention a mother-and-daughter team: three-year veteran Sally Burton of Severna Park and her daughter, Sarah, a theater arts major and frequent attendee who was visiting during a college break.

"When Sarah went away to school, I had to find something, and this wonderful group of women pulled me in," Sally said. "Now I'm addicted to singing."

And Nancy Harring of Severna Park — at 75, the oldest member of the chorus — was chatting everyone up as she handed out Christmas ornaments that went unsold at a recent holiday concert.

But like barbershop itself, the evening was deceptively serious. The women gathered in a circle and did a variety of stretches ("music comes from the body, and if the body isn't loose, it won't make good music," Craven said), navigated some voice-loosening acrobatics and, with an exacting-but-friendly Bosna at the helm, engaged in a variety of harmonizing techniques.

In four-part harmony, it's essential that everyone singing one part hits the same note at the same time — and enunciates, shapes and holds those notes in the same way.

It's among the many subtleties on which the group will be judged when it performs at the annual regional competition in Ocean City this April, an event it has never won but that has seen it improve its score every year since Bosna took over.

If it were to take first place among the groups in its size, it would receive an invitation to the 2012 international convention in Denver this fall, an event most of the 23,000 Sweet Adelines in some 500 chapters around the world would like to attend.