Benedicte Jourdois is doing many things at once.

She is playing piano vigorously, loud enough so the sound adequately fills the rehearsal space. She is keeping a close eye on conductor Maurizio Barbacini. She has her antennae raised to detect the various vocal gestures and nuances emanating from the singers. And she is following director Stefano Vizioli, who starts and stops, dashes across the floor to one singer then another, offering advice about this or that.

It’s a complicated scene with many moving parts. In the center of it all is Jourdois, rehearsal pianist and vocal coach, diplomat extraordinaire.

This opera production (the “Mese Mariano”— “Le Villi” double bill) isn’t the only Spoleto Festival event she’s working on. Jourdois is preparing to perform in two Intermezzi recitals and the second Spoleto Festival USA Orchestra concert featuring John Adams’ “Harmonielehre.” What’s more, she is standing in for the orchestra during rehearsals for the Verdi Requiem.

Despite her on-stage appearances, Jourdois mostly is a behind-the-scenes musician, expert at working with singers on musical interpretations and diction. She has a profound empathy for singers.

“It’s really hard to be a singer. My heart goes to them. I want to help them,” she said quickly, in superb English, her French accent coloring the words as if with a smooth brush, her curly black locks bouncing with each gesture. “I love working with younger singers. They need to be taught a lot. It’s very satisfying.”

She’s been a professional vocal coach for eight years now, and she’s seen singers go from amateur status to big opera companies — a satisfaction that affirms her work.

Coaching requires finesse; singers can be sensitive souls. She offers criticism in the form of suggestions or ideas. If she hears that a singer is having trouble with a particular passage, she’ll strive to offer musical alternatives — for example, subtle changes in phrasing or dynamics that make it easier for the singer to get through the passage while upholding the composer’s wishes and conveying the meaning of the text.

“I’m pretty blunt, but respectful,” Jourdois said.

Sometimes she runs interference when disagreement flairs between singers and conductors or directors. She is the one, after all, who understands the vocalists best and can defend them. On one or two occasions, when the conductor took the music too fast for the singers, Jourdois discreetly pulled back the tempo at the piano. On other occasions, she will work with receptive conductors and directors to make adjustments that accommodate the singers. Sometimes her job entails calming singers down, or letting them vent frustrations.

“All love me because I’m on everybody’s side,” she said.

To prepare for vocal coaching, especially when she’s working on an opera, she will practically memorize the vocal score in advance, and study the full score, too, so she knows the true nature of all the musical cues.

The task causes her to think like a conductor, and to learn from the conductors she works with, she said.

With a good conductor, her piano playing is like dancing, “following the lead of someone with really great musical ideas,” she said. “It can be extremely exhilarating.”

Opera, she added, is the ultimate art: It incorporates all the elements of music and theater. When the full orchestra joins the rehearsals, Jourdois can remove herself from the piano bench, but she cannot relax. Then her job is to take notes for the conductor, tracking any musical issues that arise, both in the pit and on stage.

Soprano Jennifer Rowley, who sang the leading role in both “Mese Mariano” and “Le Villi,” said Jourdois was an essential and higly respected colleague.

“She’s the glue,” Rowley said. “She’s an orchestra. That’s how I describe her.”

Indeed, Jourdois can play with intensity. No music seems to intimidate her, whether it’s a reduction of a complicated orchestra score, a delicate French chanson or the relentless arpeggios of a John Adams piece.

At the opera rehearsal, she didn’t miss a note, and only glanced at the score. Her eyes focused mostly on the singers and on the maestro; all the while her fingers flew up and down the keys, driving the music forward, lending musical excitement to what otherwise might have been a dreary slog through the blocking of the show.

“We need a big piano sound,” Rowley said. “Otherwise we tend to hold the voice back.” And that can add unnecessary strain. “Because she plays so orchestrally, we are really able to sing with our full voices from Day One.”

Jourdois plays not only with fervor, but with nuance and color, Rowley added.

I don’t think it’s something you learn. I think it’s something inside of you.”

The two women met in the fall of 2012 when, at the recommendation of a friend, Rowley scheduled some coaching with Jourdois. The soprano needed to work on her French.

“If I’m having a problem with something, I can say, ‘Benedicte, come here.’ So she will explain it in a way a singer understands.”

So you are getting the idea: Jourdois helps singers sing, understand and pronounce correctly another language and internalize a particular musical style. She does it all with patience and enthusiasm, with passion and calm attention.

“She’s a good colleague,” Rowley said. “And in our business, being a good colleague goes a really, really long way.”

Diane Richardson, a vocal coach at Juilliard who has been affiliated with the Spoleto Festival since 1977, was among Jourdois’ teachers. She called her former pupil “vivacious” and possessing “a great deal of passion” and having a sincere “love for the art form.”

It was Richardson who first invited Jourdois to the festival in 2011, to work on a production of Mozart’s “Magic Flute.”

Since then, Jourdois has returned twice, to help prepare the Chinese opera “Feng Yi Ting” last year (among other obligations), and to work on various programs this year. Almost certainly she will be back again.

Richardson said her young colleague possesses an innate curiosity and an instinct about orchestration, one that allows her to open a score in her mind and express its nuances with only her fingers.

“She brings heart to what she does,” Richardson said.

Jourdois, who was born and raised in Paris, moved to New York City in her early 20s to study, began collecting various honors and gaining invaluable experience, then found work with the Houston Opera and Pittsburgh Opera. Before long, she was principal coach and assistant conductor at the Philadelphia Opera and a vocal coach on the faculty of the highly regarded Curtis Institute.

She’s done other things, too — summer festivals, coaching at the Manhattan School of Music and, lately, spending a month or so in Charleston each spring.

While working on “The Magic Flute,” she met and fell in love with a German trombonist, Martin Vittenberg, who was playing in the orchestra. Charleston, therefore, has special meaning for Jourdois.

The couple will return together in November.

To get married.

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