All operas make extraordinary vocal demands. But for some operas in particular, the vocal fireworks are practically the raison d'_tre. Donizetti's La Fille du R_giment and Mozart's Die Entf‹hrung aus dem Serail, both opening this month, each pose significant challenges of style, stamina, and sheer vocal prowess. The sort of dazzling singing featured in these works is often compared to the high-wire act at the circus, but a better comparison is to figure skating, where powerful athleticism combines with artistic impression. But while the figure skater gets those two elements scored separately, for the opera singer, the technical and the artistic must be fused seamlessly.

"The body and voice must be completely connected," says soprano Diana Damrau, who has thrilled Met audiences in stratospheric vocal roles for the past few seasons and who returns in the fall for her first Lucia di Lammermoor. "The state the body is in has great influence on vocal production: they are one and the same." Damrau appears this month as Konstanze, whose high-flying aria was comically decried by the Austrian Emperor Joseph II as having "too many notes" in the movie Amadeus. Tenor Matthew Polenzani, who plays her love interest in Mozart's youthful comedy, describes the physical requirements of this style of singing. "It's extremely athletic," he says. "Singing requires the use of lots of muscles, big and small. And most singers sweat quite a bit while they're doing what they're doing."

But the physical demands of this kind of rapid-fire vocalism are just one factor. Difficult collections of notes cannot merely be strung together. "Technically, you must learn each note individually, then as a complete phrase," Damrau says. "Then, when you truly know it, you must trust your ears and body and go for it. Artistically, you have to look upon the coloratura writing as more than just fast notes. Each phrase and ornament has a meaning and it is up to you to interpret that meaning in your performance."

A strong legato: the smooth binding together of notes to make a beautiful phrase: is an important aspect of coloratura singing and prevents the quick dispatching of notes from sounding mechanical. Polenzani stresses that focusing on the legato from the start is essential. "I always think in terms of line when I'm learning a part: that's where legato comes from, so that's where you have to start. After the vocal line is in my voice, I consider the phrasing, and that is the way I'll think about it when I'm performing."

For Natalie Dessay, the French soprano who created a sensation as the title heroine in Donizetti's Lucia di Lammermoor this season, balancing these elements takes time. "I read the text first, then the music, then I put it together," says Dessay, who returns to the Met this month in Laurent Pelly's new production of Fille, opening April 21. "I don't want to add everything all at the same time. It takes me months and months to have [a new role] first in my mind, then in my body."

Pelly's production was a smash hit when it opened last year in London, noted for Dessay's hilarious performance and co-star Juan Diego Fl‹rez's effortless way with his main aria's infamous nine high Cs: the same aria that made Luciano Pavarotti a star. Fl‹rez agrees with the soprano that all the physical preparation is merely the point of departure, that the goal is to find the soul of the music beyond the pyrotechnics. "It's in the colors, the shading, the high notes, the legato singing," he says. "You start pianissimo and go to forte, then back to pianissimo again. You sing very long phrases. There's a lot of sentiment under these beautiful melodies, and you have to really deliver the message and the words."

The message Fl‹rez refers to reminds us that all the technique and physical agility of the coloratura singer must serve an even greater purpose. A computer can make "perfect" sounds, but opera, at its best, is supremely human. As Polenzani says, "Hopefully, by the time you're ready to walk onto the stage, you won't be thinking about technique: you'll only be thinking in terms of what you're communicating."

Reaching the audience in this way is the final step in making a great work of art come to life. The demands are mental, physical, and also very much in that indefinable category we call artistic. "Everything you need is there in the music and words," says Damrau. "You needn't look any further. But," she adds, "the two do not always tell the same story. Very often the text is very simple, and the music will say so much more than the text. So there are many, many levels. And, then, your body can say something else still. These many different layers build a character."

La Fille du R_giment opens on April 21. Die Entf‹hrung aus dem Serail opens on April 26.