Brown noise is a type of sound signal that contains a mix of frequencies, with more energy at lower frequencies. It is often described as sounding like a deep rumble or a soft waterfall. The name comes from Brownian motion, which refers to the random movement of particles in a fluid, reflecting the way the sound is generated. Many people use brown noise for relaxation or to help with sleep, as it can mask other sounds and create a calming environment. It is different from white noise, which has equal energy across all frequencies, making it sound more hissing or static-like.