A study revealed that cottontop tamarins listened to a variety of music (Bach, Led Zeppelin, Miles Davis, etc.) but only calmed down when listening to Metallica.
Like in music, in human speech, changing the tone of one's voice, the rhythm, pitch or speed allows one to gauge the emotional state of the speaker. For example, we use long tones for calming a baby while using short tones to indicate seriousness. The study found that monkeys, "interpret rising and falling tones differently than humans."