A MARTÍNEZ, HOST:
In 2007, two singers from two different generations and musical backgrounds came together to create one of the surprise hits of the year. Robert Plant is the legendary singer who fronted Led Zeppelin. Alison Krauss is a star of bluegrass and Americana music. And their album "Raising Sand" was a side project that turned into a blockbuster. It won six Grammys, including album of the year. Now after 14 years, Krauss and Plant are back.
(SOUNDBITE OF SONG, "CAN'T LET GO")
ROBERT PLANT AND ALISON KRAUSS: (Singing) Told you baby one more time don't make me sit all alone and cry. Well, it's over. I know it, but I can't let go.
MARTÍNEZ: The new album is called "Raise The Roof." And NPR Music critic Ann Powers is here to tell us all about it. Ann, 14 years - why would they wait so long?
ANN POWERS, BYLINE: With "Raising Sand," Plant and Krauss not only created something fresh and original for themselves, they shook the genre of Americana to its core. They changed the genre in a way. They had such tremendous success that I think it was just overwhelming, and the idea of trying to replicate it seemed impossible. I recently spoke with Plant and Krauss, and here's how they put it.
ROBERT PLANT: Maybe it was the overwhelm of it all and the idea of, whoa, how did we do - how did that happen?
ALISON KRAUSS: And, you know, you don't want to repeat yourself.
MARTÍNEZ: Ann, how did they finally get back together?
POWERS: They never truly separated as a duo. They continued talking and trading songs back and forth over the years. But it wasn't until Alison suggested this song by the Tucson band Calexico that the two heard something that inspired them to head back into the studio.
(SOUNDBITE OF SONG, "QUATTRO")
PLANT AND KRAUSS: (Singing) In the hills where the tall weed grows, hands are tied and won't let go. Can't escape this place.
MARTÍNEZ: All right, Ann, so is the new album worth the wait?
POWERS: I'm going to say something radical. I like this record better than "Raising Sand." It will satisfy anyone who loved that album. Both were produced by the legendary T Bone Burnett, and many of the same musicians appear. But there's a subtle expansiveness to this music that reflects what both Krauss and Plant were up to during this time, exploring everything from classic country music to global sounds. I'm particularly excited by the presence of several songs representing the English folk scene of the 1960s where Plant started before he was in Led Zeppelin. Here's one by Bert Jansch, and Alison is singing the lead. And it's just so beautiful and haunting.
(SOUNDBITE OF SONG, "IT DON'T BOTHER ME")
KRAUSS: (Singing) You gaze upon my troubled life, but it don't bother me what you see.
MARTÍNEZ: Right now, we're in a cool collaboration era in music, and that spans all kinds of different genres. But why do you think this particular pairing, Plant and Krauss, works so well?
POWERS: Not to break it down in gender terms, but the brain that Robert Plant brings to this project, he has one of the most curious minds in popular music. The brain Alison Krauss brings to the project is one of an incredibly skilled singer. She's just a master harmonizer, and together, they have that thing. T Bone Burnett calls it the third voice that comes out when you're harmonizing with someone. It's just magical. It's a once-in-a-lifetime collaboration or, you know, I guess twice in a lifetime.
MARTÍNEZ: Right. Well, twice is nice. NPR Music critic Ann Powers, thank you very much for joining us.
POWERS: Thank you so much.
(SOUNDBITE OF SONG, "IT DON'T BOTHER ME")
PLANT AND KRAUSS: (Singing) You twist my words like plaited reeds. Transcript provided by NPR, Copyright NPR.