Headphones required. Just babbling brooks, no voice.
Here's a little something I made for myself, but I thought I'd share. This file uses isochronic tones, modulation of the volume at regular intervals, to attempt to entrain a specific frequency of brain wave in the listener's brain. It also takes a step further and uses one frequency for the right and another for the left. The file is designed to deeply relax the more emotional right hemisphere and merely soothe the more logical left hemisphere. All of this relies on really soft science so any result might be pure hypnotic placebo. In fact, in a small percentage of the population with right-left swapped brains it may make people more moody and emotional.
Left Ear / Right Hemisphere - 7.5 Hz Theta (Deep Relaxation)
Right Ear / Left Hemisphere - 12 Hz Alpha (Light Relaxation)