Music director Christoph Eschenbach conducts the NSO 2010 season opening concert. (Margot Schulman)

At the end of May, when the National Symphony Orchestra was winding down its season and preparing for its current South American tour, Christoph Eschenbach, the orchestra’s music director, conducted the suite from Richard Strauss’s opera “Der Rosenkavalier.” This is sublimely rich and frothy music, like Mexican chocolate, and it’s the kind of thing in which Eschenbach revels. At some points, he turned his whole body to face the first violins, the instruments with the most rewarding melody, and moved his arms as passionately as if he wanted to plunge into the music and help wring it from the page himself.

Turning his back on the other sections can impact how well the sections are able to play together. His yearning to be part of the music can affect how clearly he is able to lead it. But there is no question that his whole heart is in what he’s doing, and that he expects everyone else onstage to be just as involved as he is.

And there’s also no question that his commitment is having an effect on the orchestra.

“I’m so appreciative of how invested he is emotionally in every piece that we play,” says Marissa Regni, the orchestra’s principal second violinist. “Whether or not you agree with his interpretation, his heart is just in every note. It’s very inspiring.”

“I definitely think morale is the highest it’s been at least since I’ve been here,” says Nurit Bar-Josef, the orchestra’s concertmaster, who came to the NSO in 2001. “He’s done really good things for us.”

Howard Mitchell, Music Director during the 1959 tour. (Miller of Washington)

Indeed, there’s a transformation taking place at the NSO. A conductor who was widely viewed as damaged goods when he arrived in 2010, and an orchestra not generally ranked as one of the United States’ marquee ensembles, seem to be embarked on a happy marriage, with a sense of optimism about the future. And some of the changes that are happening will have a profound effect on how the orchestra sounds for years to come.

The changes are relatively subtle. Eschenbach, 72, isn’t the type to try out new kinds of performances, banter with the audience or think up attention-grabbing variations on the standard concert format. His musical passions are meat-and-potatoes orchestral fare: Beethoven, Strauss, Schumann. “I think what Maestro Eschenbach brings to this orchestra is deep knowledge of Germanic repertoire,” says Lambert Orkis, the NSO’s pianist. It’s not just the NSO that’s affected by Eschenbach’s tastes; the conductor is also music director of the Kennedy Center, and this spring’s festival called “The Music of Budapest, Prague and Vienna” — which sounded like a festival of music that orchestras play all the time — reflected Eschenbach’s input.

But he leavens his musical diet with unexpected quirks: contemporary European composers such as Jorg Widmann; or a dance suite from Bernstein’s “West Side Story” on the orchestra’s first recording in years, which Orkis calls “one of the very best that we have done” (and, he adds, “I had the privilege of playing it with Bernstein”).

And in his own way, he’s throwing himself wholly into reanimating the orchestra: rehearsing energetically, playing chamber concerts with his musicians, going to fund-raising events with patrons. This last is a part of the job in the United States that most European music directors tend to loathe, but Eschenbach embraces it: “I meet very interesting people,” he says. People tend to respond in kind. “Our board is in love,” says the orchestra’s executive director, Rita Shapiro.

The orchestra is responding, too. If you can carp at the technical sides, you can’t argue, as Regni says, with the involvement: The players’ is rising to match his own. “Concerts have been pretty much on fire,” Bar-Josef opines. Indeed, observes the Kennedy Center’s president, Michael Kaiser, “the much-maligned Budapest-Prague-Vienna festival turned out to be very, very interesting, because of him.”

People are even noticing. When Eschenbach took over in 2010, there was so little national interest that no paper outside Washington, nor even the normally ubiquitous Associated Press, sent a reviewer. But two years later, at a concert performance of Bartok’s “Bluebeard’s Castle” during the abovementioned festival, critics from the New Yorker, the Philadelphia Inquirer and the Los Angeles Times all were present. They saw quite a show. “The National Symphony Orchestra seems to be on an upswing,” Alex Ross wrote in the New Yorker.

The most important changes of all, however, involve personnel. As often happens when a new music director comes in, a number of senior players have opted to retire — creating room for some long-needed upgrades in the winds and brass. The principal trumpet, horn and flute positions are all currently open, while the principal trombone and percussion chairs will be occupied by newly hired players in the fall — and at a time when many orchestra musicians are faced with salary cuts, the NSO is safely enfolded in the Kennedy Center’s sheltering arms, making it an attractive berth.

NSO's South America Tour Booklet from 1959 (National Symphony Orchestra)

“In two years,” Shapiro says, “he has hired seven players and tenured one, and there are three principal openings. He’s really overseeing and selecting and building that way, making enormous change in the sound of the orchestra.”

“Orchestras adapt to the personality of the conductor,” Eschenbach said, speaking by phone the week before the orchestra left for South America. “[The] Berlin [Philharmonic] played very, very differently with [Herbert von] Karajan than with [Claudio] Abbado or [Simon] Rattle. So this orchestra is tending now towards my way. ‘My way,’ ” he added, breaking into a few bars of the Paul Anka song, chuckling, before adding quickly, “But it is also their way.”

It can take a while to fill a new position, especially since Eschenbach tends to have a very particular idea about what he’s looking for. Instrumental color is important to him; he also places a premium on players listening to each other, rather than simply following his baton. “There’s a lot of chamber music going on,” says Nurit Bar-Josef, the orchestra’s concertmaster.

His specificity drives some musicians crazy. Eschenbach talks a lot in rehearsals, and has the orchestra play phrases over and over to get the effect he wants. Preparing for the South America tour, he had the orchestra spend almost two rehearsal sessions on Tchaikovsky’s Fifth Symphony — a piece so familiar to orchestra musicians, Bar-Josef observes, that if you “wake us up at 2 a.m., we can play that piece.” Many musicians in Philadelphia or at the Chicago Symphony, which Eschenbach led as music director of the Ravinia Festival from 1994 to 2003, felt they were above this kind of thing, and there are some NSO musicians who don’t warm to it, either. But “I think this orchestra has been eager to try something new,” Bar-Josef says, and “although there may be some people who are still unhappy, there are certainly a lot of happy people.”

The tour, the orchestra’s first international excursion with a music director of its own in nearly a decade, should make people happier; at least, it got off to a good start in Mexico City, where according to different headlines it either “seduced” or “conquered” the public. South America is a friendly place for this maiden voyage; no major U.S. orchestra has toured this region for nearly a decade, and audiences are excited.

Even lasting change may not be enough to elevate the NSO to the uppermost echelons of U.S. orchestras. But Eschenbach appears to be looking for slow building rather than a stardom that may in any case elude him. He remains the highest-profile conductor the NSO has had since the days of Mstislav Rostropovich, and at the helm of the NSO, he seems, after a long period of feeling underappreciated, to be having fun.

“Before I began here,” he said, “I thought it would take longer to get the orchestra sort of out of its cage. To let them have fun with music. I thought that process would take longer, and it didn’t.”

How does he feel about the position now? “It’s better than I thought,” he said. “More enjoyable than I thought. I’m very happy with it.”