Frank Loesser's "Most Happy Fella," at Dicapo Opera Molly Mustonen, right, and Michael Corvino performing in "The Most Happy Fella" at the DiCapo Opera Theater. The Dicapo Opera Theater's delightful production of "The Most Happy Fella," Frank Loesser's tender, tough and melodically soaring 1956 work, boasts something no musical currently on Broadway can offer: natural sound. Amplification has long been standard practice in musical theater. True to its identity as an opera company, Dicapo presents the winning cast and orchestra in this production without any electronic boosting. Dicapo's 204-seat auditorium can seem almost too intimate in operas like "Tosca." But what a great space for this classic American musical. The original Broadway production starred the operatic baritone Robert Weede as Tony, the middle-aged Italian immigrant vineyard owner in Napa, Calif., in the late 1920s. In Dicapo's staging the baritone Michael Corvino brings a robust voice and disarming vulnerability to the role. The gruff yet kindly Tony falls for a harassed young waitress in a San Francisco restaurant. He leaves her a note and begins a courtship by mail. The sweet-voiced and lovely soprano Molly Mustonen is wonderful as Rosabella, as Tony affectionately calls the waitress. We find out that she is actually called Amy. When it was new, "The Most Happy Fella" started a critical debate about whether it was a musical or an opera, and the question lingers. Inspired by the Italian element of the story, Loesser, who wrote the book, lyrics and music (based on Sidney Howard's play "They Knew What They Wanted"), created an intricate, quasi-operatic score. There are melodies that befit opulent operatic voices, as well as trios and quartets in which individual characters voice their inner thoughts. For me, a music drama is a musical when words have slightly the upper hand in the score, as Loesser's lyrics do here. The piece is ill served if operatic voices milk the melodies at the expense of the text. This cast made every word matter, for which the director Michael Capasso and the conductor Pacien Mazzagatti deserve credit. What a pleasure to hear Ms. Mustonen filling Rosabella's arching melodic lines in the wistful "Somebody, Somewhere" with her shimmering voice, while making the words come through so conversationally. Mr. Corvino brings both a Verdi baritone richness and a crisp articulation of the character's broken English to the title song, "The Most Happy Fella," when Tony receives a promising letter from Rosabella, with an enclosed photograph. One slight dramatic flaw in the casting is that Tony is described in the book as old and unattractive, especially by his possessive sister, Marie (here Bess Morrison). Mr. Corvino's Tony looks like a distinguished middle-aged gentleman. It is a hard to imagine that no woman in Napa saw this lonely, big-hearted vineyard owner as a good prospect. Still, the plot hinges on Tony's deception of Rosabella, which registers powerfully here. Afraid to send her a photo of himself, he sends one of his burly, good-looking foreman, Joe (the strong baritone Peter Kendall Clark). When Rosabella arrives, having agreed to marry Tony, who has just injured himself in a reckless truck accident, the humiliated young woman impulsively marries him anyway. But in a weak moment that night, she succumbs to Joe's advances. Over time Rosabella, nursing Tony, falls for him. They start over their courtship in the endearing duet "Happy to Make Your Acquaintance." For all the operatic trappings of "Happy Fella," the gritty first scene is right out of Broadway. The Texas transplant Cleo (the sassy Lauren Hoffmeier), who works as a waitress with Rosabella, complains about her job in "Ooh! My Feet! Loesser spikes her whining melody with pinched, dissonant chords. The stage direction is traditional, lively and effective. The orchestra plays from the back of the stage, behind a scrim, which allows the theater's small pit to be covered, giving the cast more room to twirl and shimmy during the dance numbers, deftly choreographed by Francine Harman. The orchestra was not relaxed enough in the score's most Broadway-styled stretches. But any little shortcoming is nothing in comparison with the joy of hearing this Loesser masterpiece in an intimate, acoustically natural setting. Take that, Broadway. "The Most Happy Fella" runs through Sunday afternoon at Dicapo Opera Theater, 184 East 76th Street, Manhattan; (212) 288-9438, dicapo.com.