Thirty-four songs into their first of two consecutive nights at the Smoothie King Center this weekend, the members of 311 found their voice. More specifically, they found the Voices of Peter Claver.

There is a redundancy to the 311 catalog that becomes all the more obvious during 311 Day, a marathon concert staged every two years on March 11 (and, this year, on March 12 as well).

Songs often follow a standard blueprint: similar tempos, guitar tones, rhythms and arrangements, with vocalist Nick Hexum’s steady, dancehall-inflected voice featured until rapper S.A. Martinez jumps in.

That pattern was repeated frequently on Friday — not that the hardest of the hard-core fans in attendance seemed to mind. But they also heard something different. In addition to beefed-up lighting and lasers, 311 Day inevitably includes surprise guests. On Friday, those guests were two dozen white-robed choir members from St. Peter Claver Catholic Church in Treme. They absolutely elevated the band and the show.

Gospel music is not necessarily in 311’s DNA. The band formed in Omaha, Nebraska, in the late 1980s to intermingle alternative rock, hip-hop and reggae.

The worldwide community of 311 fans comes together every two years for 311 Day. The tradition launched at the State Palace Theater on Canal Street in 2000. It graduated to the Lakefront Arena and then the even larger Smoothie King Center. New Orleans has hosted seven of the nine celebrations to date.

In 2014, the single-night 311 Day featured a staggering 66 songs spread across five hours, with two intermissions. Breaking this year’s 311 Day into two nights meant Friday’s show consisted of “only” 40 songs in three hours, with one intermission. Hexum and his bandmates intended not to repeat any material on Saturday, so fans who attended both nights would hear about 80 songs.

The arena’s upper bowl was mostly empty on Friday, but the lower bowl and standing-room-only floor were packed.

An opening video montage announced that fans had traveled to New Orleans from all 50 states and foreign countries ranging from Australia to Paraguay. The montage also featured video greetings from ordinary fans around the world, “Modern Family” co-star Eric Stonestreet and members of No Doubt, Incubus, Deftones, Slightly Stoopid and other like-minded bands.

After a crunchy guitar intro, the five members of 311 jumped into the set with “Hive.” “Hive” exemplified the hip-hop/hard rock hybrid at the heart of 311’s sound, and it served as a statement of purpose for all that followed.

“Come Original,” a standard of 311 sets, preceded “We Do It Like This,” which, according to setlist.com, was last performed 14 years ago.

After “Flowing,” a highlight of the 1999 album “Soundsystem,” they debuted a new song, “Hey, Yo.” Hexum’s and Tim Mahoney’s guitars harmonized as Martinez sang in his upper register.

“Never Ending Summer” stuck to the 311 formula; the vintage “Summer of Love,” with its pop chorus, did not. The crowd pogoed furiously throughout the heavy “Freeze Time.”

During “Who’s Got the Herb?” — the herb in question is not oregano — scores of fans toked up, as if the arena’s smoking ban was temporarily suspended. “Omaha Stylee” signaled the end of set one. “We’re going to go catch our breath,” Hexum said. “We’re just getting started.”

Twenty minutes later, they returned with “Homebrew.” The reggae opening of “Don’t Tread on Me” gave way to Mahoney’s hard-rock riffage. Peaks and valleys came and went — “Amber” was chill; “Jackpot” was up-tempo — but all stayed within the lines 311 has drawn for a quarter century. During “India Ink,” Hexum’s airy vocals contrasted with hard-working Chad Sexton’s heavy drums and Mahoney’s metallic chords.

Mahoney dressed up several songs with short, richly toned solos. But only bassist Aaron “P-Nut” Wills got his own extended showcase. Armed with a six-string bass, he popped and plucked his way through a seven-minute solo excursion. Using foot pedals and loops, he built a melodic, all-bass cover of Daft Punk’s “Get Lucky.”

Wills’ solo also gave the Voices of Peter Claver time to get situated onstage. They introduced themselves with “When the Saints Go Marching In.” When 311 joined them for the 2009 single “It’s Alright,” it was as if we’d all been transported to another show with a different band. Bolstered by the choir, “It’s Alright” blossomed into a big hug of a pop song with a glorious, sunny chorus.

A guest keyboardist provided another fresh, and welcome, wrinkle in “I’ll Be Here Awhile.” The keyboardist, choir and Mahoney, working with an especially flattering arrangement, made the Coldplay-esque “Tranquility” soar.

“Journey in peace now,” the voices sang, “you don’t have to be afraid.”

That closed the second set. Moments later, 311 returned to the stage to once again be 311. Much to some fans’ disappointment, the 311 Day setlist in 2014 omitted the hits “Down,” “All Mixed Up” and “Come Original.”

That mistake wasn’t repeated. After opening the encore with “It’s Getting OK Now,” they concluded with three signature songs: the heavy “Feels So Good,” the nimble “Don’t Stay Home” and a final “Down,” arguably the most successful distillation of the 311 formula.

More of the same, and likely more surprises, awaited on Saturday.

Follow Keith Spera on Twitter, @KeithSpera.