diapason vs folk song

diapason

noun
  • The musical octave. 

  • The range or scope of something, especially of notes in a scale, or of a particular musical instrument. 

  • A harmonious outpouring of sound. 

  • A tonal grouping of the flue pipes of a pipe organ. 

folk song

noun
  • folk music 

  • A song, in any folk style, originating among ordinary people, usually non-professional musicians, and handed down by oral tradition. 

  • A song in the style of folk music, a modern genre of popular music. 

How often have the words diapason and folk song occurred in a corpus of books? (source: Google Ngram Viewer )