It's been nearly three weeks since 10-year-old Jackie Evancho took the nation's breath away on NBC's " America's Got Talent." Her version of "O Mio Babbino Caro" from Puccini's opera "Gianni Schicchi" brought the house down and assured her a place in Tuesday night's semifinals.

And sure enough, within minutes of her performance, the Internet was alight with people insisting the young girl was lip-synching. The rumor mill was running at such a furious pace that on the next evening's results show judge Howie Mandel asked Evancho to sing a few notes on her own to prove it was really her voice that audiences were hearing.

Adding to the conspiracy theory cause late last week, sister shows " Britain's Got Talent" and "X-Factor" admitted that they use Auto-Tune technology to enhance voices for, they say, the television viewer's entertainment experience. The American arm of the producer, Fremantle Media, says it doesn't use pitch-altering devices for any part of "America's Got Talent — a moot point in the end since a quick trawl of YouTube for early Evancho performances shows there wouldn't be much need to tune her voice.

"America's Got Talent" vocal coach Yvie Burnett has been working with Evancho since June to make sure she's comfortable on stage. "What strikes me about [Jackie's voice] is that it's not too heavy.

"You sometimes hear young children, and they're trying too hard. With Jackie she just opens her mouth and out it comes."

Her remarkable sense of pitch is one of the many things that makes Evancho's talent so exciting to audiences. While children, or anyone for that matter, can be taught to match pitch, singers with a natural ability to do so have a huge advantage.

Perhaps a reason some find Evancho's talent so difficult to believe is that audiences are simply unused to this sort of sound from a child. But it's not unheard of: as a young girl, Julie Andrews sang operatic repertoire with a similar sound. That's partly because her teacher was an opera singer but also because that light classical style was popular in the '30s and '40s with the music hall audiences whom her parents were entertaining.

In modern America, most young singing talent tends to imitate pop stars rather than opera singers. YouTube is full of pint-sized belters doing their best to imitate their heroes. ( Justin Bieber, anyone?)

The difference between Evancho and fellow Pittsburgher Christina Aguilera is how they produce their sound. A pop voice is "like revving a motorcycle," says Anne Tomlinson, music director of the Los Angeles Children's Chorus. "The sound is produced right on the larynx. In bel canto, which is actually the technique opera singers use, the breath is used to support the voice like water supports a boat."

Evancho's coach may be teaching her the bel canto technique, but calling her an opera singer would be like saying a sixth-grader who is exceptionally good at throwing a football is ready for the Steelers.

There's more to being a quarterback than throwing a 40-yard pass, and similarly, opera takes years of practice on top of the raw talent. A woman training to be an opera singer doesn't develop her voice fully until she is at least in her mid-30s. It takes that long for the voice to completely mature and for a singer to learn how to reliably access the full power and range of color her instrument offers.

"[The voice] needs to be able to function as it is and at the stage of development it's at," says Mike McCarthy. As music director at the National Cathedral in Washington, one of McCarthy's main responsibilities is training the child sopranos to sing in the traditional Anglican men and boys choir. "There is a question of the development of the voice in its more natural form, and by natural I don't mean like an innocent, sort of treble white — I just mean as it matures, it doesn't try to sound too old, doesn't try to imitate the sound of an older singer."

It is on this point that people who have a lot of experience with children's voices start to worry about Evancho. A person gets only one voice, and if it is improperly developed, it will become irreparably damaged. Charlotte Church, the Welsh soprano, was enormously popular through her teens singing exactly the same repertoire Evancho favors. Now in her mid-20s, the novelty of her age has worn off and Church's voice is no longer impressive enough to sustain a career.

The difference in Evancho's voice between her YouTube audition video and her first "America's Got Talent" performance is telling. While singing César Franck's "Panis Angelicus" for the audition, Evancho sounds very much like an Anglican cathedral chorister. The sound is pure, the vibrato is natural, her pitch is spot-on, and there is no audible break in her voice. In "O Mio Babbino Caro," her voice is much darker, more grown-up-sounding but also more forced. There is also an audible break in her voice, which makes it sound as if she is not strengthening her vocal cords in all registers equally.

Carol Tingle is a Los Angeles-area voice teacher who has been instructing private students since 1966. "Technically what's she's doing is lowering her larynx to get that opera sound. Singers are incredible imitators of sound. It wouldn't surprise me if she hasn't listened to many opera singers, so what she'd be able to do is adjust the larynx and imitate the sound she is hearing either recording or by her coach."

All children imitate their heroes, whether it's basketball or singing. A good teacher will make sure pupils channel that enthusiasm into finding their own style. In Evancho's case, her teacher has an additional challenge: safeguarding that voice.

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