Good news for skeptics: modernist music can be beautiful. If what keeps listeners away from the “difficult” music written in the past century is a fear of dissonance, they can rest assured. If such American mavericks as Conlon Nancarrow and Charles Wuorinen can produce so many moments of beauty, stillness, and humor, and if virtuosos like Ursula Oppens and the JACK Quartet can realize those moments as brilliantly as they did last Sunday, surely audiences will come around.

As it was, a decent-sized crowd came out for Sunday’s concert at (Le) Poisson Rouge, one of New York’s premier “club” venues for classical music. Just four works occupied the evening: Wuorinen’s Piano Quintet, his solo piano piece Oros, Nancarrow’s String Quartet no. 3, and his Two Canons for Ursula. With so many new music concerts devoted exclusively to world premieres, it is wonderful to have older modernist works get more performances too, so that they can become part of the language we expect from the concert hall.

It was the New York premiere of Wuorinen’s Oros, whose title means “mountain” (and many other things) in Greek. The piece begins and ends with four repeated low Cs (the base of the mountain?); in between, it leads us through a lyrical, rambling collection of little phrases. Moods linger for only a moment, with some phrases amplifying others that came before, and some seeming to come from the clear blue sky. Oppens, a veteran of the new music scene, deftly handled the piece’s technical challenges and guided listeners through Wuorinen’s strange landscape. Through her expertly judged phrasing, the piece’s tiny episodes came together in a coherent musical arc. The work was surprisingly dancelike, with a transparent texture.

Nancarrow’s String Quartet no. 3 was a beautiful contrast to the expansive Wuorinen. A true iconoclast, Nancarrow devoted almost his entire composing life to a single musical structure: the polyrhythmic canon, in which the canonic voices move at different speeds. His music became so rhythmically complex that he couldn’t find musicians who could play it, leading him to largely abandon composing for live instrumental performance and write almost exclusively for the player-piano. For all that, his music is upbeat and even fun, like ragtime on acid. He is unafraid of both polytonality and traditional diatonic harmonies (i.e., consonance); the most challenging thing about listening to him is those unexpected rhythms. As Frank Zappa said, “You’ve got to hear it. It’ll kill you.”

The String Quartet no. 3, one of Nancarrow’s few works written for a traditional performing ensemble, is ferociously difficult, with each movement a canon of six beats against five, against four, against three. At the end of the work, all four voices accelerate at different rates while staying in these proportions, before ending on the same note. The first movement begins and ends with a lively, aggressive cello line, the other voices building hairpin crescendi and decrescendi with their own canonic entrances. The second movement was a string of shimmering high harmonics in offbeats with each other, with pizzicati falling like raindrops on a wooden windchime. The third movement returned to the imitative style, this time with lots of slides, a fury of pizzicati, and fast, long bows, leading into the folklike harmonics again, before rushing to a busy, oddly funny climax. The JACK Quartet, dedicated to new and contemporary music, did a great job with the work, letting listeners forget about technical challenges and just fall into Nancarrow’s world.

Written for Oppens in 1989, the form of Two Canons for Ursula suggests a party trick, but the results are expressive and lively. In the first canon, all the lines are elaborated from a few melodic cells, with tempos played at ratios of 20:25:28:35. In the second, the right hand enters a third of the way through the piece, playing the same canonic line one and a half times faster than the left. The two hands meet at the conclusion. Nancarrow punctuates the canon with unison octaves, lending structure to the jazzy restlessness of the piece. Oppens rendered the intricate counterpoint with pinpoint clarity, but also judiciously phrased the canonic lines to lend them shape and direction.

The evening concluded with Wuorinen’s Piano Quintet, a richly varied work ranging from violently independent lines, dramatic unison moments, unexpectedly quiet lyricism, and plaintive swoops. As in Oros, small gestures either went by in a flash or built up into a complex, powerful whole. The JACK Quartet lost many strands of bow hair in their vigorous playing, and Oppens played as if she were a longtime member of the group. It’s not music whose meaning is especially obvious, and it surely takes several listenings to learn the language. But with such expert performers, it’s a journey worth taking.