An interesting (though not particularly surprising) article on MSNBC's Cosmic Log relates a recent experiment:
"Cotton-top tamarin monkeys grew calmer after they heard music based on their own calm, friendly calls. But the monkeys became more agitated when researchers played music that contained elements of their own threatening or fearful calls."
From the mp3 samples provided, it sounds like they're using granular synthesis to make randomized loops of the audio.
