There are definitely two Florence Welches. One is the quiet, slightly awkward woman you meet backstage, in dressing rooms strewn with flowers and fabrics. In conversation, she's eternally, empirically British, reserved to the point of distance, whispering and always folding herself inward, as if she's trying to reach into that formidable set of lungs to find the right words. If it wasn't for her flame-red hair and striking, alabaster skin, she'd almost disappear into the background. And you get the feeling that she'd probably like to.

The other Welch is the one you see onstage: ethereal, epic, seemingly channeling something from another place. There are moments, when she's really blowing and she opens her eyes wide, that you get the sense even she can't fathom the power she's channeling or the places she's letting it take her. She is a great singer, from a different era -- and not just, like, the 1940s. Maybe the 1800s. Or medieval Europe. There would be flowered wreaths involved. The phrase "madrigal" comes to mind. You know.

It's not uncommon for performers to completely transform the minute they step beneath the spotlight; it's practically a necessity. Singing is, by its very nature, a rather unnatural endeavor, and singing before an audience of people, well, that's about as much of an out-of-body experience as there is. Going to that other place is less of a coping mechanism as it is a flat-out survival skill, it would seem.

But it's rare that you see two sides of the same person during one performance. Last December, at New York's Angel Orensanz Center (a perfect venue), was one of those times. Welch was both the damsel and the demigod during [article id="1682255"]her taping of MTV's "Unplugged,"[/article] whispering her way through between-song banter one minute, belting so hard she lifted the rafters the next. Maybe it was the intimate nature of the show -- surely having Kanye West sitting 10 feet from you would have an effect of some sort -- or perhaps she was summoning the spirit of the place, but you'd be hard-pressed to find a more perfect Florence and the Machine performance.

Of course, Florence the Former, being the church mouse she is, summed it up thusly:

"It was really wonderful. But what to say in between? I got so bashful. I was so grateful to be there, and I was trying to express that, and it just went into this weird, stilted speech. Singing is fine. Talking, not so much."

She's not kidding, either. Before taking on Otis Redding's "Try a Little Tenderness" -- which, you're probably aware, Kanye sampled on the Watch the Throne standout "Otis" -- she turned to West and muttered, "This is my favorite song ... I think ... um, yeah, hopefully it won't go as well." Speech is not her strong suit.

But singing definitely is. And it's readily apparent in "Unplugged," which premieres Sunday at 11 p.m. ET on MTV. From the hushed, chill-inducing "Tenderness" (one of two covers she does; the other is a rather tidy little duet with Josh Homme on "Jackson") to stirring, stripped-back takes on newer tunes like "Never Let Me Go" and "Only If for the Night" and set-closing hit "Dog Days Are Over," Welch's lofty range is on display throughout. And so is that ability to seize emotion from thin air. You will get goose bumps, that much is sure.

And yet, that's usually the case with a Machine performance. But on "Unplugged," backed by a choir and strings, in a space first consecrated in 1850, it's all taken to another level (no wonder it's being released as a standalone album). Even if you weren't lucky enough to be in the room that night, you get the sense that you're truly witnessing something special. And when you throw in her fabulously furrowed banter (Welch definitely leads the league in "Ums"), well, then you get the other side of the coin too. Which is what makes it perhaps the definitive Florence set. Or at least the most personal. She truly was made for "Unplugged," even if half her personality wouldn't agree with that assessment.

Then again, that duality is what makes all the great ones great. Welch never gets down and dirty the way singers like Nina Simone or Etta James did (it's something you feel in your gut), mostly because it's not in her wheelhouse. Instead, she floats above it all, goes higher (and subsequently deeper) than you'd think possible. And it's fitting. After all, on this night, she was singing in a synagogue. And as we know, Welch is most definitely a proper girl. Some of the time, anyway.

Don't miss Florence and the Machine's "Unplugged" on Sunday at 11 p.m. ET on MTV.