fade out vs let up

fade out

verb
  • To slowly disappear. 

  • To fade from a cut to black in a movie. 

  • To decrease in volume, such as at the end of a song, until there is only silence. 

noun
  • A type of transition used in film, usually at the end of a scene, involving a fade to black from the cut. 

let up

verb
  • To cease or stop. 

  • To cease or stop (doing something intense). 

How often have the words fade out and let up occurred in a corpus of books? (source: Google Ngram Viewer )