Brown noise is much nicer than white, especially if you apply an exponential smoothing to it (there are examples on youtube, look for smoothed brown noise). I a

Brown noise is much nicer than white, especially if you apply an exponential smoothing to it (there are examples on youtube, look for smoothed brown noise). I attached a speaker to a raspberry pi and use its hardware random number generator to make that sort of noise. It's a pleasant, smooth rumble that I leave on all night. I certainly find it helps a lot (I'm prone to insomnia) and I'd be astonished if it's having any negative physiological effect.