Why rain helps you fall asleep
Rain barely changes: an even rustle with no sharp sounds or pauses. It covers street noise and the neighbours, and gives your mind nothing to catch on.
Its spectrum is close to pink noise, so people often play rain instead of noise: it's soft and sounds natural.
How this rain differs from a recording
It's not a recording but synthesis: the rustle and drops are generated in your browser on a loop almost a minute long. So there are no ads, no cut at the end of a video and no thunder to wake you.
How to listen
Quietly, like rain behind a closed window. Keep the phone or speaker away from your pillow. Set the timer for 30 to 60 minutes and the rain fades out on its own.