muffled vs unheard

muffled

adj
  • Stifled or covered up; diminished by interference. 

unheard

adj
  • Not heard. 

  • Not listened to. 

  • Not known to fame; not illustrious or celebrated; obscure. 

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