The way I understand some of these thingies is that they are just bineural beats with a fancy name. Bineural beats - a certain frequency through one headphone and another through the other one. The brain compensates the difference by producing brainwaves at the specific differential frequency. Using this technique you can make the brain produce certain brainwaves and thus make it go into a certain state. Alpha, beta... So relaxed state, "meditative", "dreaming"... As far as I know it's proven that your brainwaves do change when you do this. Anyone feel free to correct me if I said something wrong.