The chamber ensemble Either/Or, which performed Feb. 18 at the Library of Congress. (Julieta Cervantes / )

Since 2004, the chamber ensemble Either/Or has championed contemporary and experimental music, premiering 125 new works along the way. On Saturday at the Library of Congress, the New York-based group offered a cross section of its repertoire in a performance that was spot-on focused and unfaltering but, at times, unforgiving.

Violinist Jennifer Choi and the ensemble’s director, pianist Richard Carrick, opened the concert with Anthony Braxton’s “Composition No. 222.” The duo started out in unison then diverged, creating a disquieting undertone, not unlike watching a person tottering along the edge of a ridgeline.

Carrick returned onstage for his composition “La Scène Miniature,” a work depicting the murder scene from Albert Camus’s “The Stranger.” Featuring flutist Margaret Lancaster, cellist John Popham and bass clarinetist Vasko Dukovski, the quartet re-created the narrative in a visceral way, generating sounds ranging from groans and sighs to insects buzzing and aircraft diving.

In Anna Thorvaldsdottir’s “Ro,” Icelandic for “serenity,” percussionist Russell Greenberg used a gong, wood blocks, crumpled paper and other instruments to create myriad sounds under Carrick’s baton. With Dukovski, Lancaster on bass flute and a piano quintet (Choi, Popham, violinist Pala Garcia, violist Erin Wight and pianist Taka Kigawa), the meditative work flowed out of airy breaths to conjure echoing bagpipes and a brassy organ in an entrancing way. If “Ro” was calm and evocative, then Beat Furrer’s rhythmic “Spur” was percolating and roiling, with the piano quintet’s plucky strings attacking with urgency. That energy carried over into the D.C. premiere of Furrer’s cacophonous “Intorno al bianco.” But despite the wind and string players’ heroics, especially in cascading glissandi, the net result was an aural onslaught 15 minutes too long — a reflection of the composition, not the musicians.

Five of Gyorgy Ligeti’s piano etudes rounded out the program and were handled with technical brilliance by Kigawa and his velvety smooth pianism.