Since the founding of the Orchestre Septentrional in 1948, the band’s homeland, Haiti, has endured the nearly three-decade Duvalier family dictatorship, 26 other governments, a foreign intervention, a devastating earthquake and, most recently, a cholera epidemic.


Through it all Septen, as the group is known to its fans, has been that rare Haitian entity that functions flawlessly.


Onstage, whether playing an elegant ballroom or an outdoors festival in the countryside, Septen is a dynamo, with a heady combination of drums and horns driving dancers onto their feet. But to Haitians, Septen’s ability to thrive when all else seems to be falling apart makes the orchestra something more — a bulwark and a solace.


“They’ve created a community institution that is really unlike anything else in Haiti,” Gage Averill, author of “A Day for the Hunter. A Day for the Prey: Popular Music and Power in Haiti” and an ethnomusicologist at the University of British Columbia. “It’s amazing. Few countries can speak of the political swings and economic challenges that Haiti can, but here’s this orchestra that even as it changes with the times, has carved out a distinct sound and approach to music making. In terms of longevity and impact, they are remarkable.”


Though little known outside Haiti and its diaspora, Septen is enjoying a burst of attention. The band is the subject of a new documentary by Whitney Dow, “When the Drum Is Beating,” that will be broadcast nationally on PBS on Thursday night (on Sunday in New York and Los Angeles) and is in the middle of a North American tour that includes three engagements this weekend in the New York metropolitan area.


“Because music is not just a source of entertainment, but one of the primary elements within Haitian culture, it offers a different path into the country,” Mr. Dow said when asked what motivated him to make the film. “Haiti is always defined by its current problem, but by mixing music and history, you can show strengths as well as weaknesses. And Septen is definitely one of those strengths.”


Like many Haitian ensembles, Septen’s rhythmic foundation draws heavily on the complex drum parts traditionally played at voodoo ceremonies and festivals. In more recent years the band has incorporated varied guitar styles from outside Haiti, the most important being chicken-scratch funk and the light and airy patterns typical of the Francophone Afro-pop heard on Haitian radio stations.


But the band’s trademark remains its large Cuban-derived brass section. Hulric Pierre-Louis, a Septen founder and its maestro for many years, used to tell stories of how as a young man growing up in Cap-Haitien on the northern coast, he would listen to radio stations in Santiago, Cuba, on the other side of the narrow Windward Passage, and transcribe the music he heard coming over the airwaves.


“Haitian music is a blend of a lot of different rhythms and styles from a lot of places — from Africa, Europe, the Caribbean, Latin America,” said François Nikol Levy, a conservatory-trained keyboard player and arranger who for the past decade has been the orchestra’s musical director. “You’re going to hear that mélange in the songs Septen writes and plays.”


Mr. Dow’s film, shot from 2006 to 2010, captures Septen in a transitional stage. Younger players, steeped in funk and jazz, were being brought into the band to keep its sound current, and the discomfort of some of the veterans is palpable.


“Today certain people are trying to change Septen’s sound,” Michel Tassy, a singer who joined the orchestra in 1963 and is now 68, complains to the camera. “If you do that, you get caught up in the fire. I need a little respect from the institution. Without that, things won’t work.”


Mr. Tassy remains in the orchestra and still sings lead on many of its biggest hits. But leadership onstage has clearly passed to Jocelyn Alce, a bass player who says, “I am the motor of the band,” and doesn’t mind interjecting flourishes that recall Stanley Clarke or Larry Graham into the music.


At the moment Septen’s youngest member, hired in December, is a 19-year-old saxophonist. He is not on the current tour — as is the band’s custom, he is still back in Haiti learning Septen’s repertory of more than 500 original compositions, in styles ranging from fast-moving merengues to slow and romantic boleros. But he represents the fifth generation of musicians in the band, which numbers from 14 to 19; Mr. Tassy is from the second generation.