all other sounds seem to disappear?

The sound of the rain drowns them out.

And even though the sound of the rain goes on all night,

it doesn't keep you awake.

Rain is a kind of white noise—

a steady, unchanging, unobtrusive sound.

White noise is made up of sounds from all the frequencies a human ear can hear,

with the sound at each frequency having equal power.

It’s called “white” because the definition is like that of white light,

which is a combination of all the light wavelengths we can see.

You might think that a combination of all possible sound frequencies would be terrible,

but it’s not—quite the opposite.

The reason for this is that white noise masks other sounds.

Think of it like the rain:

the sound of one drop falling, like from a leaky tap,

would be very distinct and annoying.

Two drops would be the same.

You could even tell three steady drips apart.

But if there were five or 10 or 1,000,

you couldn't pick out each individual drip.

They'd all blend into a sort of hum or a quiet roar and probably lull you to sleep.

The calming properties of white noise are starting to be used to treat different problems.

White noise can help restless people sleep and help migraine sufferers sleep through their pain.

It can be very useful for people with attention deficit disorders, who have trouble tuning out background noise.

White noise can help them concentrate.

It's even used to mask the sound of individual conversations by therapists and others who want to maintain privacy.

Who would have thought that mashing lots of sounds together would actually turn out to promote peace and quiet?