You've probably heard someone swear by a fan humming in the background, or a smartphone app playing ocean waves. But lately, a more precise vocabulary has emerged for sleep sounds: white noise , pink noise , and brown noise . Each has a distinct frequency profile, a different feel, and — according to growing research — different effects on sleep quality. This guide breaks down the science and the sound of each color noise, helps you understand which is best suited to your sleep challenges, and shows you how to use them effectively tonight. What Is “Color Noise”? Sound is made of waves at different frequencies. Just as visible light can be split into a spectrum of colors, audio engineers use “color” terminology to describe how energy is distributed across those frequencies in a given sound. The key measure is spectral density — how much power a sound has at each frequency. White noise has equal power at every frequency. Pink noise boosts lower frequencies slightly. Brown (or...