This seems like an obvious selection, given that if it didn't have such a profound impact on our state of consciousness, we probably wouldn't bother. Specifically, chanting is often claimed to be particularly transcendant, presumably because the vibrations and rhythms sent throughout your body and contrast or conform to heartbeat - or so goes the theory. Probably also because it slows breathing.
I suspect that music is calming when it projects what we naturally associate with safety and balance - the absence of predators, the presence of water, the availability of food, winds to keep temperatures moderate, etc. And at some point in our history, we probably used our voices in unison to scare off predators, and started banging on logs with sticks - quite literally "whistling in the dark" and thus associate choir singing with safety and balance.
