Gentle Rain sounds for 8 hours to play all night while sleeping.

It is without doubt that the sound of rain has an effect on the body and mind. In it is healing and relaxation and tranquility.

The following information is taken directly from the website:

Article from Vogue.com:

"Rain is predictable, calming, stable, and non-threatening," says Dr. Shelby Harris, a behavioral sleep-medicine specialist. According to Harris, steady rainfall noises help lull the brain into falling asleep, block outside noises, and frequently induce a more meditative state that brings on relaxation. Though similar to the hum of white noise, rain sounds are actually considered pink noise, which is quickly becoming the new It noise color. "White noise consists of a large spectrum of all frequencies that are audible to the human ear," explains Harris. "In contrast, pink noise —though similar in sound to white noise with its consistent “whoosh”-ing noise that blocks external noises—has less of the higher frequencies. Essentially, it is deeper than white noise." While there's limited research on pink noise, a National Library of Medicine study found that it increased deep sleep and dramatically improved memory in older adults.
While rain soundtracks are a sleep time mainstay for many, it's no surprise they're seeing an uptick in interest during the pandemic. "Stress levels are high, and we have active and busy minds that are hard to turn off," says Harris. "Sometimes just going back to nature in a steady, repetitive, non-threatening sound can help quiet the active brain." And as we're spending more and more time awake, rain recordings can also help block out other noises that pose a threat to sleep. In other words, it's never too late to trade the ping of push notifications for the sweet pitter-patter of raindrops. Your REM cycle will thank you.

Melbourne University blog post:

Studies have found that when rain sounds enters people’s brain, brain unconsciously relaxes and produces alpha waves, which are very close to the state of brain when human sleeps.
Rain sound is generally between 0 and 20 kHz. It is not upsetting. On the contrary, this sound makes people comfortable. However, if there is a sudden sound of thunder in the middle of rain sounds, it will make people stressful. At the same time, the level of cortisol in people’s body will be high.

Reference:
https://blogs.unimelb.edu.au/sciencecommunication/2019/08/27/why-do-people-sleep-better-when-it-rians/
https://www.vogue.com/article/rain-sounds-for-sleeping#:~:text=%22Rain%20is%20predictable%2C%20calming%2C,state%20that%20brings%20on%20relaxation.