Christina Aguilera is, first and foremost, a Vocalist with a Capital V. Last week, in order to announce hew new album Liberation, she released a new song "Accelerate". Produced by Kanye West, the song a pretty crowded number, and that means it doesn't give Aguilera's greatest asset – her voice – any room to stretch out.Some people were pleased about that (her ad-libs and growls have been known to grate), while others felt it was a shame. Those in the second camp will be happier today, due to the release of "Twice," the second new track taken from Liberation. It's a ballad completely in Aguilera's wheelhouse, and showcases her voice, which sounds as good as ever. It's also the total opposite of "Accelerate" in that its production is actually pretty minimal: Aguilera is accompanied only by a piano, but her warm tone more than fills any gaps, and she really does feel at her best when she's just left to sing. And yeah, maybe there is a growl or two, but it wouldn't be an Xtina ballad without them, would it?Follow Noisey on Twitter.