If you haven’t been listening to pop radio in the past few months, you’ve missed the rise of two seemingly opposing trends. In a medium in which mediocre singing has never been a bar to entry, a lot of pop vocals suddenly sound great. Better than great: note- and pitch-perfect, as if there’s been an unspoken tightening of standards at record labels or an evolutionary leap in the development of vocal cords. At the other extreme are a few hip-hop singers who also hit their notes but with a precision so exaggerated that on first listen, their songs sound comically artificial, like a chorus of 50s robots singing Motown. The force behind both trends is an ingenious plug-in called Auto-Tune, a downloadable studio trick that can take a vocal and instantly nudge it onto the proper note or move it to the correct pitch. It’s like Photoshop for the human voice. Auto-Tune doesn’t make it possible for just A. He went out of fashion soon. B. He had to give up Auto-Tune. C. He became very successful. D. He held concerts worldwide.