calmly vs sotto voce

calmly

adv
  • In a calm manner. 

sotto voce

adv
  • Speaking quietly. 

  • Sung or played softly, instruments or voice. 

noun
  • A direction in a score that a passage in a piece should be played softly, or sung in a low voice, when applied to vocal music. 

adj
  • Soft, instruments or voice. 

  • In soft tones; quiet. 

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