White noise

Equal power at every frequency: the bright hiss of an untuned radio.

White noise has the same power at every frequency. Since there are many more high frequencies than low ones, it sounds bright and hissy, like steam or a detuned TV. Here it is limited to 20 Hz–16 kHz, which covers what nearly everyone can hear.

It masks the widest range of sounds, which makes it the classic choice for covering voices, snoring or a neighbour’s TV. If it feels harsh after a while, try pink noise.

Using it for a baby? Keep the phone across the room, not in the crib, at a low volume (why).