“The Sound of Music Live!’’ is just that.

It’s decidedly not a remake of the 1965 movie. Carrie Underwood is not trying to be Julie Andrews, nor is Stephen Moyer trying to be Christopher Plummer.

No one is making that mistake.

Rather, NBC’s three-hour production at 8 p.m. Thursday is intended as an event, the sort for which people once gathered around a television instead of catching up with on their phones.

Underwood, like most folks, grew up watching the movie.

“I don’t think I could remember the first time I saw it,’’ she says on a break from rehearsals.

Tucked away in a ballet studio in lower Manhattan, the cast worked for four weeks before heading out to a Long Island set to rehearse another two weeks until the big day.

Wearing hot pink leggings, a gray sweatshirt and green sneakers, but in full makeup because of a morning talk show appearance, Underwood smiles as she says, “This was one of my mom and dad’s first dates. My mom is coming up in a few weeks, and she is incredibly excited.’’

“It’s been lovely, treating this like a proper show,’’ Moyer says, sprawling on a club chair.

It’s been 18 years since he did a musical. Though “a massive Christopher Plummer fan,’’ Moyer says, “I will try to make myself different. I don’t think he’s (Captain von Trapp) very likable in the beginning. I want him to be cold and broken. He’s retreated into being an officer and a captain of the fleet. His way of controlling everything is to have it be neat and tidy, and everything is until this little firebrand arrives.’’

When executive producers Craig Zadan and Neil Meron approached her to play Maria, Underwood recalls thinking, “This would be awesome. Then, did that just really happen? And, what did I get myself into?’’

As daunting as performing live is, just making the commitment to doing it was what first dogged Moyer.

“Whatever happens — if I go reeling down the stairs, or I gash my head open, it doesn’t matter,’’ Moyer says. “I said yes, and that’s the beauty of it.’’

Between “American Idol’’ and years of concerts, Underwood is experienced at singing live, but she’s done little acting, and this is her first lead. A great short-term memory, which made cramming for tests easy, helps in learning lines, she says.

“I have been finding a lot of similarities between myself and Maria,’’ she says. “Her love of grass and trees and space. That’s where she can be herself, in nature. I was a farm girl and singing, and I was always outside.’’

“Maria is not a refined girl,’’ David Chase, the show’s musical director, says. “She is a rural girl.

“The power of the story is how the sound of music changes people and opens the heart.’’

This live version is based on the 1959 Broadway musical, which starred Mary Martin. Initially, Martin had asked Rodgers and Hammerstein to write a song. They signed on because they were so taken with the true story of the novice nun who became nanny to the motherless von Trapp children, then wife to the captain.

Chase opens a binder with the show’s sheet music and turns to the most famous song. Here, Maria sings, “My day in the hill has come to an end, I know. A star has come out to tell me it is time to go. But deep in the dark green shadow, there are voices that urge me to stay. So I pause and I wait and I listen, for one more sound, for one more lovely thing that the hills might say.’’

Then Underwood launches into “The hills are alive with the sound of music.’’

The two songs most different from the movie version are “My Favorite Things’’ and “The Lonely Goatherd.’’ That last one, not surprisingly, is Underwood’s favorite.

“I have been yodeling my whole life,’’ she says.

“The structure is different,’’ says Christian Borle, who plays Max. “People who grew up knowing the movie will be very surprised by the song order, and I found the whole thing to be very moving.’’

Borle, who won a Tony and has spent a lot of time on stage and on TV with “Smash,’’ says this production is a wonderful mix of the two.

“This has never been really done, not in this day and age,’’ Borle says. “It is a hybrid.’’

“It has its own strange quality to it,’’ he says. “I find it fascinating performing a musical with no proscenium. With this we are going to have cameras all over the place, trying to capture the proper style. You have to act and suddenly sing and keep it really for television.’’

A mountain with grass was being built for the set, and it is there that Liesl (Ariane Rinehart) will sing “Sixteen Going on Seventeen.’’ The Barnard College junior had played two of the younger von Trapps in St. Louis productions.

“I really feel like I have grown up with the kids,’’ she says.

And most people feel they have grown up with “The Sound of Music.’’

Now if Zadan and Meron can capture the magic of a live performance for TV, a new generation will have the experience, and Underwood predicts copycats will try other live versions.

“There is an immediacy to the live shows,’’ Zadan says.

Live shows such as the Oscars, which they produced, attract the largest audience.