The legendary rapper, Tupac Shakur, made an appearance at Coachella in California last weekend, in spite of the fact that he's been dead for more than 15 years. He performed on stage alongside Snoop Dogg, including a "live" shout-out to the Coachella audience. Putting aside the creepy factor of performing with dead singers, let's talk briefly about the technology. Let me say at the outset that even though I was...