i bought this app..actually a few of them. I have no idea if it actually works, but it is interesting to listen to. Kinda a lot of pitches or the same weird pitch. You can get the app and play around with it to check it out. It makes sense in the context of maybe stimulating or calming the brain.
itunes has apps quite a few on this stuff. i bought a few of them untill i realized there was one with alot of choices. The one to make you fall asleep did work. I am not sure if it was the app itself or the monotone sounds. I remember the secret they talked about holosync stuff but that was extremly expensive so I never followed up with that.