The Lydian String Quartet is full of surprises. Friday, before the group’s concert began at Lippes Hall in Slee Hall, the lights dimmed. The good-sized crowd sat in hushed anticipation. From backstage, we heard the sounds of tuning, then a raucous laugh. We all looked at each other. What were we in for?

The musicians trouped out, a bit informal, a bit flustered. They sat down. And a transformation came over them, as they eased, impeccably, into Beethoven’s “Harp” Quartet.

Later we were told the raucous backstage laugh had probably come from the cellist, Joshua Gordon. He has a loud, deep voice. But the amazing thing was, whatever the musicians’ personalities were outside of the music, they checked them at the door. As they played, they were focused, in tune and of one mind.

The witty and beautiful “Harp” quartet showed the delicacy of their playing. The coda to the first movement had a zest and a magic — enough so that the audience applauded afterward, a trend that mysteriously continued throughout the concert’s first half. The rapid third movement was full of fine interplay among the instruments.

For the record, violinist Judith Eissenberg could not make it to the concert because of an arm injury. Boston violinist Danielle Maddon filled in. Besides Gordon on cello, the other two Lydians were Daniel Stepner, playing first violin, and violist Mary Ruth Ray.

The Quartet in G, Op. 18, No. 2 was immediately engaging.

Stepner proved himself throughout the evening to be a stellar leader, articulating his lines with ease, depth and emotion. He brought such energy to the finale that by the end, his bow was in shreds.

The quartet is capable of subtle gradations in volume. The passages of exquisite quiet were especially thrilling. The balance among the instruments was also exemplary. No one drowned anyone out. Everyone could be heard.

These strengths all combined to make the concluding Quartet in C Sharp Minor, Op. 131, a satisfying journey. This quartet is a tough nut to crack. It’s all over the map, both in mood and in melody. It is to the Lydians’ credit that they made it relatively accessible. Your mind didn’t wander, listening to this group.

In the Lydians’ hands, the knotty, unruly Op. 131 had an improvisational feel. Aggressive rhythms on the cello gave the first movement color and life, and Stepner did a good job shaping his tricky melodies. The phrasing was sometimes percussive, sometimes surprising — the pizzicato notes on the cello seemed to pop out at you — but the ensemble’s singleness of purpose and fine sense of timing made it work.

All in all, a fulfilling performance of a challenging program.

Concert Review

Lydian String Quartet

Friday night in Lippes Concert Hall in Slee Hall on University at Buffalo North Campus, Amherst.