I have never ever, ever heard Britney Spears sing without a track, what about her concerts you say? If you think that she really sings live when she is in concert then you are a bigger sucker than I thought you were. Britney doesn’t sing live because she can’t sing, the proof is in this video from The X Factor in which Britney tries to sing Happy Birthday to La Reid doing what I’m assuming is her impression of a good singer.