falsetto vs hissing

falsetto

noun
  • The "false" (singing) voice in any human, usually airy and lacking a purity of vowels; created by utilizing the next highest vocal folds above those used for speech and normal range singing. It is commonly confused with the head voice register. 

  • A person who sings in falsetto. 

verb
  • To sing or utter in falsetto. 

hissing

noun
  • The sound of a hiss. 

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