Your favorite ASMR playlist probably isn’t true white noise—or brown noise or pink noise, for that matter.

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.”)[…]

Continue reading: What Exactly Is White Noise?