Naturespace audio has developed the most realistic 3-D nature sounds I've ever heard. The relaxing nature sounds seem to be above, below, behind, and all around you. It is available as a smartphone App, or you can listen to them on your speakers (available on iTunes). If nature sounds aren't as helpful for you, click here for other suggestions for audio sleep aids.
Naturespace "provides an audiophile-class listening experience to all headphone users, including earbuds...It is a truly profound new way of listening to the natural world". You listen to them, preferrably, with headphones. A few are suitable for speakers.
The remarkable thing about Naturespace, versus other nature sound choices, is that the "3-D sound field is captured with accurate depth, distance, space and position".
My twin sister told me about it last month when I was under a lot of pressure for many weeks to fulfill a challenging obligation. Some days the stress was nearly overwhelming. I got the Naturespace App and immediately felt more relaxed and the obligation I was working on felt much more doable. I listened to it in the background for days. I still listen to it often simply because it is so beautiful and relaxing.