striking new collaboration between ex-Zep singer Robert Plant and bluegrass star Alison Krauss is not as unlikely as it seems, as they tell Neil McCormick Free download: Get 'Killing the Blues' from the new album 'Raising Sand' Robert Plant picks up my recording device, a mischievous twinkle in his eye. "I have one of these for vocal ideas," he says. "But I never use it." And now for something completely different: Plant and Krauss So what do you do? "I just wait until the tape starts running and then go, 'Oh baby, baby…'?" Plant sang the word "baby", or variations...