White, pink and brown noise

The colours describe a spectrum, not a brand. White, pink and brown noise all contain every audible frequency at once, and what separates them is how the energy is distributed across those frequencies. White noise is flat, equal power in every band, which the ear hears as bright and hissy because human hearing is more sensitive up top. Pink noise falls off at roughly 3 dB per octave, which lands closer to how we perceive loudness and comes out sounding balanced, like steady rain. Brown noise falls faster still, so most of the high end is gone and what remains is a low rumble, closer to a waterfall heard through a wall.

What the evidence for sleep noise actually supports

Mixed, and worth saying plainly rather than burying. Some work points at steady sound shortening sleep latency or deepening sleep, other work finds nothing, and the studies that do find something tend to be small. The claim that survives is the least exciting one: constant sound masks variable sound. A quiet room is only quiet until a door slams, and it is the contrast that pulls you up. Raising the noise floor with something steady flattens that contrast, which is why noise helps most on a busy street, in a hotel or next to a snoring partner, and does very little in a bedroom that is already silent.

Preference matters more here than theory. Plenty of people find white noise abrasive and sleep fine to brown. Some cannot sleep with any sound at all. If it stretches out how long you take to drop off, or you keep noticing it, it is not working, and that is reason enough to turn it off.

Tock ships 63 fall-asleep sounds and lets you layer four at once and save the mix, so brown noise under rain under a fan is one screen rather than three apps. Most of them are generated on the device sample by sample rather than played back from a file, which means nothing loops and no two nights sound identical, and an audible loop point is exactly the sort of detail that snags attention during a nocturnal awakening. The full set lives on the sounds page, and the rest of the bedroom setup sits under sleep hygiene.