Octarium continues to refine its sonority and musical profile, and its distinguished concert on November 14 and 15, Modern Masters, showed that the group is gaining heft with leading choral composers around the country as well. The program included two world premieres and marked the release of a CD by the same title containing the music performed at these concerts. The eight-voice choir, which is led by Krista Lang Blackwood but sings without a conductor, had solicited works from several top composers that they, the composers, felt should be better-known than they are. The project yielded some rare beauties, as well as a couple of pieces that have perhaps remained obscure for a reason. What struck me most at the concert, which I attended at Corpus Christi Catholic Church in Lawrence, was how evenly balanced the voices were across the sections; the group seems to have overcome an earlier tendency toward top-heaviness.

Pied Beauty was a new version of a piece that composer Mark Adamo had long felt needed revision, and its reworking was quite lovely. Cast as a series of excursions from tonality that eventually work back toward a restful diatonic center, the piece shows a keen sensitivity to text-setting. Morten Lauridsen’s Contre Qui, Rose is cut from the same gorgeous sonic cloth as his better-known O Magnum Mysterium, but it is a pretty low-key affair that, for me, lacks a sense of forward motion; it never “breaks out” to achieve anything resembling a goal-point. (A movement of a larger work, it works more effectively in the context of the whole.)René Clausen’s Set Me as a Seal and Daniel Gawthrop’s Lo, How a Rose were among the more conventional, even mundane, works on the program; Steven Stucky’s Eyesight had at least a deft sense of climaxes.

Eric Whitacre’s A Boy and a Girl, a setting of a classic miniature by Octavio Paz, presents the tripartite statement with breathless simplicity and grace. In Octarium’s rendering it began to drag toward the end, and the super-pianissimos were nearly drowned by the church’s heating system. Leah Hamilton Jenkins showed off a gutsy soul sound in Stephen Hatfield’s Double Shot, a straightforward gospel tune that interweaves images of Moses in the desert and Christ on the cross. In Gawthrop’s Sing Me to Heaven the sense of over-refinement got a bit out of hand; there is a fine line between polish and preciousness, one that Octarium, happily, seldom crosses.

Three moments stood out at this concert. Steven Paulus’ i carry your heart with me might be faulted for containing music less adventurous than the e.e. cummings poem, but here it was the perfect marriage of score and performance: The warm, unfussy rendering brought out the best in these eight singers. Libby Larsen’s Four Valentines: A Lover’s Journey showed the group’s ability to sustain a large-scale work — rather refreshing on a program consisting mostly of three- and four-minute miniatures. In the Still Garden was sung with rich personality, despite some very subtle tuning issues. St. Valentine’s Day played whimsically with rapid-fire staggered entrances, and Will You, Nill You was imbued with a sort of comic urgency. But Shakespeare’s lush verse in Shall I Compare Thee to a Summer’s Day? led Larsen perilously close to treacle.

The piece that stood out most on this program was the dazzling On Green Mountains by Steve Danyew, a young composer who won the 2009 Octarium Composition Competition, and who is, according to stevedanyew.com, a Master’s student at the Eastman School of Music. To a stark, crystal-clear poem by Ashley Garofolo, this startling piece evokes autumn in Vermont — or so the composer has written, though its images of fragrant morning chill and small-town America are something most of us can connect with. It begins with a cushion of high, austere female voices, on which the men sing “Green mountains,” and moves almost impressionistically through a quiet, tranquil autumn landscape. Its counterpoint is at times so spare as to evoke Renaissance or even Medieval polyphony. The mood grows more vigorous for the central strophe (“music on the green, down the street…”), then returns to the cluster-cushion of the opening for “Morning — chilled and grey.” After a final glow of bright sunlight comes a friendly foreboding of winter. On Green Mountains is a seven-minute gem of sensitivity, skill and tremendous sophistication, fully worthy to appear on a program of the best living American choral composers.

The singers of Octarium are sopranos Renee Stanley and Ashley Winters, mezzo-soprano Andrea Coleman, alto Leah Hamilton Jenkins, tenors Jay Van Blaricum and Jason Parr, baritone Brady Shepherd and bass-baritone Benjamin Winters. Modern Masters, as well as Octarium’s previous CDs, can be purchased at octarium.org. Also search Octarium at iTunes.com andrhapsody.com.

To reach Paul Horsley, send email to phorsley@sbcglobal.net.