The four women of the Real Vocal String Quartet know they have something rare and unusual going, but it wasn’t until they answered a last-minute call to collaborate with the Canadian singer/songwriter Leslie Feist that they fully realized the singular nature of the ensemble.

Launched almost a decade ago by Berkeley violinist Irene Sazer, the RVSQ started as a vehicle for her stylistically expansive tunes and arrangements. But with a bevy of the region’s most versatile musicians as collaborators, the group gradually took on a collective identity.

Featuring violinist Alisa Rose, violinist/violist Dina Maccabee, and cellist Jessica Ivry, the RVSQ celebrates the release of its second album “Four Little Sisters” (Flower Note Records) Saturday at Freight & Salvage.

With a program ranging from Regina Spektor’s “Machine” and Gilberto Gil’s “Copo Vazio” to David Byrne’s “Knotty Pine” and Duke Pearson’s “Sweet Honey Bee,” the album encompasses an astonishing array of traditions reconfigured by the quartet’s hardy mélange of conservatory chops, roots soul, and sumptuous vocal harmonies, all laced with improvisational brio.

“When the first CD came out, most of it was my stuff and it really reflected a body of work, either originals or arrangements that I had written,” says Sazer. “But I had envisioned that it would be a truly collaborative project, and you can really hear that evolution on the new CD. I have to work hard to get a word in edgewise musically now, and I love that.”

Nothing better illustrates the quartet’s unique skill set than the collaboration with Feist. The invitation to join her in the midst of creating her acclaimed 2011 album “Metals” at a studio in Big Sur came out of the blue, when someone recommended the group to her manager.

“It was super random, just getting mentioned down the grapevine,” Maccabee says. “I got this email that said I’m Feist’s manager looking for a string ensemble familiar with folk and pop, but that can also improvise. It was like a description of us.”

“In our fantasy we thought wouldn’t it be amazing if they recognized we’re creative artists, not just sweeteners for a rock album,” Sazer says. “We didn’t want to get our expectations high, but then we’d start doing something and they’d be amazed. We felt like we were doing things that are very easy because we improvise together all the time. After a while Feist suggested we try singing too, and we did a lot of back up vocals for her. It was so much fun, such a high.”

Leslie Feist: collaborated with RVSQ. Photo: Duane Storey

Feist has hired the quartet for several high profile gigs, including a CBC performance, Coachella and an appearance on The Tonight Show, earning the ensemble some welcome international attention. While RVSQ recordings capture some of the group’s energy, you have to see the women in action to fully appreciate the way the group weaves everything together. Singing and bowing simultaneously is no simple feat. Sazer and the quartet up the ante with foot stomps and percussive taps, knocks and slaps.

A founding member of the jazz-steeped Turtle Island String Quartet, she helped create string techniques for playing rhythm parts, often called chopping. Always looking to expand possibilities for string players, Sazer likes to point out that drums are often made of wood with skin stretched on top, which also nearly describes a violin or cello.

She puts her jazz training to use in other ways. At just about every show the group plays several spontaneously generated improvisations, a practice they call “now.” One player starts and the others quickly join in, creating brief, lapidary interludes.

The quartet’s huge range of influences makes perfect sense considering Sazer’s resume. She earned a bachelor’s degree from the Peabody Conservatory of Music in the early 1980s and spent the first part of her career in the classical world, performing with the Oakland and San Francisco Symphonies, and serving as concertmaster of the Bay Area Women’s Philharmonic. But Sazer could never settle into one style. Over the years she’s recorded with everyone from Ella Fitzgerald, Frank Sinatra and Ray Charles to Ali Akbar Khan, David Grisman and Bjork. The RVSQ shares the same restless musical curiosity.

“What’s really exciting is that we all have so many different influences, Irish, Balkan, pop, folk, rock, Cajun,” says Rose, who has also performed widely with Jeremy Cohen’s Grammy-nominated Quartet San Francisco, another stylistically expansive ensemble. “I think learning all these different ways to use our voices is the coolest thing. I love being exposed to all these different styles, but it can be challenging to find the connections.”

For Sazer, the RVSQ provided a path back to composing after the birth of her two children. Until they started elementary school, she had to put writing on the back burner while focusing on being a mom and earning a living. In a moment of despair at her lack of creative outlets, she realized she needed to start composing, even if just for herself (a radical shift for a freelancer conditioned to produce on assignment).

She first connected with Jessica Ivry, a rising cello star and vocalist who performs with avant-cabaret composer and singer Amy X Neuburg and the Cello ChiXtet. She’s also collaborated with clarinetist composer Beth Custer, singer/songwriter Vienna Teng and the Balkan women’s choir Kitka, among many other ensembles and projects. Ivry brought Maccabee into the fold, and Maccabee knew Rose. Sazer didn’t set out to create an all-women group, but is delighted with the results.

“That was just the way it happened,” she says. “I can’t tell you how often I was the only woman in all male bands, so it might be in part a natural inclination. There is a comfort and camaraderie in the group. It feels like traveling with a gang of friends. We have sometimes sung with men, but there’s something that’s unique and wonderful about the blend of women’s voices.”

Andrew Gilbert, whose Berkeleyside music column appears every Thursday, also covers music and dance for the San Jose Mercury News, Contra Costa Times, Los Angeles Times, Boston Globe and KQED’s California Report. He lives in west Berkeley.