Who is a better singer, Luciano Pavarotti or Alicia Keys?

Of course, that depends on your criteria.  Pavarotti was one of the world's greatest opera singers.
His style was in the genre of classical operatic.  Keys, on the other hand, sings in the popular style
of blues.  In that genre, she is just as accomplished a singer as Pavarotti. 

The two figures below are spectrograms of passages from their music that will be compared and
contrasted in the class.   These spectrograms are graphs of the time changes in tones in the music
(the fundamental pitch tones as well as the overtones).   Click on each image to watch a YouTube
video of the spectrogram being traced out as the music is played.

Luciano Pavoratti (from aria Nessun Dorma)           

Alicia Keys (from song If I Ain't Got You)