sough.

Sough is an online sound generator designed to help relax, concentrate, and mask over any distracting noises from the surroundings. Depending on the type of sound, background noises can be distracting or even calming. The regular whirr of a fan, the gentle patter of rain against the window or the constant buzz of a white noise machine are sounds that many people find relaxing. Even the distant rumble of thunder can be soothing when you’re comfortable and safe indoors.

If you need to focus…listen to white noise
To calm down…try brown noise
To fall asleep faster…try pink noise
For study sessions…try green noise