When people mention white noise these days, they might be talking about any continuous noise that blocks out other sounds or just seems soothing. Strictly speaking, however, a playlist of LEGO bricks calmly clinking in the background isn’t technically “white noise.”

As Live Science explains, white noise is a combination of all the sound frequencies humans can hear—about 20 to 20,000 hertz—played at the same amplitude. Frequency, which essentially describes how many times a wave repeats itself per second, determines how high- or low-pitched a sound is. Amplitude, or the height of each wave, corresponds to volume. Picture a piano with a separate key for every single pitch a human can hear; if you could hit all those keys repeatedly with exactly the same force (so no single key was louder than another), you’d have something akin to white noise.

Pink Noise vs. White Noise vs. Brown Noise

White noise is so named because it’s basically the aural equivalent of the color white, which is a combination of all the light wavelengths humans can see. But it’s not the only colored noise out there.

Even though every frequency in white noise has the same amplitude, the human brain is known to be more attuned to higher frequencies—so higher-pitched sounds in white noise may seem slightly louder than their low-pitched counterparts. In other words, some people might think white noise sounds too tinny or whiny to be soothing. So audio engineers have created a variety of other types of noise that help mute that effect.

Pink noise is also a combination of all audible frequencies, but the amplitudes of the frequencies decrease as the frequencies increase. The result is a deeper, softer stream of noise that sounds a little like a rainstorm. The amplitudes in brown noise are lowered even more, giving it a bassy, rumbling tone. Brown noise, by the way, has nothing to do with the color—its namesake is Robert Brown, a 19th-century Scottish botanist who studied the random, ceaseless motion of microscopic particles. (That motion is known as “Brownian motion,” and brown noise is also sometimes called “Brownian noise.”)

Can White Noise Really Help You Sleep?

While some small studies have suggested that white noise (or other colored noises) can help you drift off to dream land and stay there, it really depends on the person. “Biologically, you don’t need this [sound] to sleep,” Michael Grandner, director of the University of Arizona’s Sleep and Health Research Program, told TIME. “And if you use it every night, you can get so used to it that you can’t sleep without it.”

That said, white noise can definitely help block out other sounds that wake you up or keep you from falling asleep in the first place. As the Sleep Foundation explains, the reason a creaky stair or car alarm might cause you to stir is less about how loud that sound is and more about how sudden or inconsistent it is. Since white noise is continuous—and incorporates all detectable frequencies already—other sounds get lost in it.

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