For all the high-tech, three-dimensional highjinx involved with “U2 3D,” make no mistake about it — the title’s most important letter and numeral are U and 2.

The digital 3-D effects might attract attention, but its the band and its songs that make this a concert documentary that’s almost as good as the real thing.

The movie is cobbled together from several South American shows during the Irish megagroup’s 2005 “Vertigo” tour. Even in front of oceans of fans undulating inside mammoth soccer stadiums, the band seems bigger than life. The movie doesn’t overdo the 3-D effects, which is good because having someone sing right in your face for 90 minutes could get a little old, even if it is Bono. When he reaches out to wipe your tears away during “Sunday Bloody Sunday,” you’ll either swoon or think, “Oh, this must be the part where he remembered he was being filmed in 3-D.”

In fact, many of the shots that raise goosebumps are the panoramas of the emormous crowd — some 80,000 strong — bouncing, waving and singing. Even Spanish-speaking Argentinians know the words.

The towering stage props and video screens are evidence how times have changed since “Under a Blood Red Sky,” U2’s first concert film from 1983, but the group’s strengths are the same as they’ve always been. It’s all about the songs, and Bono and the boys — the Edge, Adam Clayton and Larry Mullen Jr. — roll through a greatest-hits catalogue. Starting with “Vertigo,” every song is a highlight unto itself: “Beautiful Day,” “New Year’s Day,” “Pride (in the Name of Love),” “Where the Streets Have No Name,” “One,” “The Fly” and “With or Without You” stand out. With arms waving in front of your face, the movie feels like a concert, which makes the $10.75 ticket price easier to swallow.

Unlike the best rock documentaries, “U2 3D” shows no behind-the-scenes footage, no interviews and nothing that might place the tour in any kind of historical context. But Bono gets his big messages across, mixing his typical religious imagery with soaring vocals, and the joy in the faces of the young people in the crowd proves that the band can still connect emotionally, with or without 3-D effects.