“The string quartet is the hardest of musical mediums,” was the favorite refrain of the late Mehli Mehta, father of Zubin, and he bestowed – or rather bellowed – it upon every student sturdy enough to survive his baton. The inherent truth of Mehta’s mantra was displayed at Tonic on Wednesday night, when Music for String Quartet made its debut.

Comprised of four veterans of the avant-garde music community, the new group produced mixed yet promising results. Jenny Scheinman, who has performed with singer Norah Jones and guitarist Bill Frisell, was joined by Carla Kihlstedt, violin; fellow Frisell alum Eyvind Kang, viola; and Marika Hughes, cello. Ms. Kihlstedt and Ms. Hughes hail from San Francisco; the latter was a founding member of Charming Hostess, the former an ex-member of 4tet San Francisco.

Sitting in the first violin seat, Ms. Scheinman was clearly in charge, with most of the material drawn from her newest solo CD, “12 Songs.” The chorale-like quality of the opener, “Sleeping in the Aquifer,” broadcast the pastel timbre that was to dominate the evening. In soft, whispering tones, bows placed over the fingerboard, the musicians struggled to coalesce in a terrain far more delicate than the electrified fields in which they normally maneuver.

In the next selection, “The Frog,” Ms. Hughes plucked an ostinato cello line, and the accompanying tremolos by Mr. Kang and Ms. Scheinman provided a perfect atmosphere over which the more assertive Ms. Kihlstedt could solo, making deft use of odd chords, slides, and harmonics.

Vocalist Jessika Kenney, a colleague from Mr. Kang’s group Secret Chiefs 3, joined the ensemble for two pieces based on Shakespeare’s “Twelfth Night.” She gave voice to the character of the clown at the end of the play. The inclusion of vocals, as well as an extended arrangement of an odd-metered duo for two violins by Bela Bartok, “Ruthenian Kolomejka,” provided a welcome respite from the otherwise more ethereal material.

Selections like Ms. Scheinman’s “The Hopper” and Mr. Kang’s “Braided Dissonance” seemed long-winded, even given their respective klezmer and bebop undertones. And the arrangements in general often failed to utilize the full range and capabilities of the viola and cello. Ms. Hughes in particular showed great restraint, pulling back the volume of her full tone so as not to overpower. But by the closing number, Ms. Scheinman’s Nino Rota-like “Wiseacre,” many of these innocent transgressions were remedied, and the four distinct voices of the group coalesced into a unified whole.

The array of disparate styles in this new quartet and the individuality of each member’s playing will provide quite a challenge in the future. In order to grow, Music for String Quartet will have to work hard to cultivate the same uniformity of sonority that every string quartet, regardless of genre, must achieve. Good thing these musicians know how to play the blues.