The all-female singing group Lorelei Ensemble makes a truly astounding sound. Each work at Rockport Chamber Music Festival on Friday, without relying on familiarity to catch the audience’s attention, reliably elicited exhalations from the crowd. The content ranged very widely, from excerpts from the oldest source of Western notated music (the Codex Calixtinus) to a 2014 commission.

The ensemble’s accomplishment is multi-faceted. First, there is its tone, a soft-edged but muscular sound. I would bet that no discussion of them at intermission was held without using the word “blend” to describe the single-mindedness of tone and execution. The voices blended thoroughly without becoming bland; while individual voices only rarely made themselves known, the summed sound underwent subtle metamorphoses which rarely surprised. Instead, a history of careful choices became apparent as the evening went on, as you realized that the sound had changed since you first started listening, without your noticing any steps in its evolution.

The evening opened with ancient music. In addition to the Codex Calixtinus came selections from the Torino Manuscript and from Guillaume Du Fay. Lorelei makes no pretense to to early music specialization. They sang with some unobtrusive vibrato and with an approach I want to call “romantic” (with a small “r”). They were sparing with dynamics and tasteful in interpretation, but perhaps the sinuousness of their lines and the gentleness of their attack discovered an intimacy in a music that I typically find otherworldly. In their hands hocketing does not “pop”, instead it is a shared nudging back and forth, almost sly.

The atmosphere thus created was convincing enough that I didn’t quite recognize the work of David Lang until the fourth or fifth close dissonance. The three movements from Lang’s recent love fail probe at the theme of heartbreak. The music is recognizably Lang, built up out of small motives that he combines using a variety of tactics, with a wide range of density. The second movement, “head, heart”, takes a prose poem by Lydia Davis that distills loss almost to storybook aphorism: “Heart weeps./Head tries to help heart.” Lang uses cannily placed and increasingly lengthy silences to create an almost unbearable tension as one awaits the re-entry of voices. Here the Lorelei demonstrated another of its powers, the ability to perform with incredible precision, with attacks and releases made sharply so as to make the silences stand out starkly.

Peter Gilbert’s Tsukumi (a Lorelei commission) afforded the singers a chance to show off another aspect of their craft: the ability to present themselves on stage in arrangements of simple, sculptural beauty. For almost every piece on the program they rearranged themselves on stage, often breaking into subgroups that stood obliquely to one another, but the eight short movements of Tsukumi called for a different picture. Based on texts from Japanese five-line waka poetry and using what the notes called “unrecognizable melodies from the Torino manuscript,” each movement featured a different member of the ensemble. Sometimes the pictures had clear functional purposes: the V-shape of the opening number made visible the way motives moved from the soloist to the ensemble, travelling down the legs of the V. There were asymmetric islands of singers in several movements; and a striking moment where the ensemble went to the back of the stage, facing away from the audience, while the solo singer moved downstage. The texts speak of the moon and of waves, floating and darkness, and Gilbert creates that world out of glissandi and declamation and streams of fluid vowels. It was an attractive series of Imagist miniatures, impeccably executed.

The second half consisted of works belonging to, or inspired by, the Sacred Harp, a tradition of mass singing with all parts sung by whoever wishes in whatever octave. The genre exists in happy ignorance (or avoidance) of proper compositional rules (one must love parallel fifths to love Sacred Harp). The adoption of that reertoire by professional vocalists can be problematic; the Boston Camerata has sung them with some success; Anonymous 4, less so. Lorelei, gorgeous, precise and striking as they had been in the first half, served the music was less well. We heard one truly traditional tune, “Africa” by William Billings, and contemporary Sacred Harp tunes by Dana Maiben, Joshua Shank, and Adam Jacob Simon. It seemed to me that the soft-edged sound favored by these voices deprived the Billings of its edges and sharp elbows, though it suited Shank’s aching love lament “Saro” (also a Lorelei commission) perfectly.

Something a bit more unusual also came in the other piece commissioned by the ensemble. Reconstructed by Joshua Bornfield is a mashup of American traditional tunes in three movements. “Wrath” is based primarily on the “Battle Hymn of the Republic” shorn of its chorus; “Brother, Sister, Mourner” uses the familiar text of “Amazing Grace” with an unfamiliar melody; and “Salvation” uses the Sacred Harp tune “Song to the Lamb”. There’s some exhilaration in the free treatment of the familiar, but the biggest choices fall flat. A “Battle Hymn” that never reaches it chorus didn’t strike me as a statement of (as the program notes have it) a “simple philosophy and [a] glorification of war”, but instead as a piece of music that lacked momentum. The extended suspension at the end of “Salvation” feels tacked on dramatically, although the sheer tonal energy of the final chords were beautiful to hear. It was a curious moment. I could feel the ensemble’s sound and presentation taking me over, even as I took notes about how I was not convinced by what the music was doing. At an early moment I had closed my eyes to concentrate on the music itself, and had been quickly bored; as soon as I opened my eyes and could see the call-and-response within the ensemble, the way they moved the rhythm and the melody among themselves, I was again engrossed. Their encore was ostensibly “Bring a Little Water Sylvie” by Leadbelly. I did not recognize it in their languorous arrangement, with its jazzy twinge halfway through each verse, but that did not diminish my enjoyment. They did all this in the almost reverberation-free Shalin Liu Performance center, producing that flawless sound without any assistance from the hall.

By the end it felt like the ensemble had been thoroughly, enjoyably dominating its repertoire. It was an impressive feat, and a pleasant evening. They will be featured at the orchestral concert at the Tanglewood Festival of Contemporary Music in August; Ligeti is on the program. I look forward to seeing them grapple with music that gives a bit more resistance than what they brought to Rockport.

Brian Schuth graduated from Harvard with a Philosophy degree, so in lieu of a normal career he has been a clarinetist, theater director and software engineer. He currently resides in Boston after spending the last 15 years in Eastport, Maine.