Because white noise contains all frequencies, it is frequently used to mask other sounds. Why does white noise drown out voices? Here is one way to think about it. Let’s say two people are talking at the same time. Our brain can normally “pick out” one of the two voices and actually listen to it and understand it. However, if 1,000 people are talking simultaneously, there is no way that your brain can pick out one voice. It turns out that 1,000 people talking together sounds a lot like white noise. So when we turn on a fan to create white noise, we are essentially creating a source of 1,000 voices. The voice next-door makes it 1,001 voices, and our brain can’t pick it out any more.