audible vs muffled

audible

adj
  • Able to be heard. 

verb
  • To change the play at the line of scrimmage by yelling out a new one. 

noun
  • The act of or an instance of changing the play at the line of scrimmage by yelling out a new one. 

muffled

adj
  • Stifled or covered up; diminished by interference. 

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