Pink noise is a type of signal that contains all of the sound frequencies that fall within the range of a human being’s hearing — from the lowest pitches that a person can hear to the highest tones. A variation of white noise, it is usually created when these audible tones are joined together at the exact same time and density. It is sometimes referred to as 1/f noise or flicker noise.
Distinct from white noise, pink noise emphasizes lower frequencies, and its amplitude drops off at a constant rate for each octave, typically three decibels. With pink signals, lower sound frequencies are usually louder and have more power than higher frequencies. In scientific terms, it has a frequency such that its power spectral density is inversely proportional to its frequency. On the sound frequency spectrum, pink falls between white and red noise, also known as Brownian noise.
To a person’s ears, pink noise is often flat, sounding like the buzz on an empty television station or the sound of ocean waves. This resonance is due to the noise being based on octaves rather than on individual frequencies. Typically, it is created by filtering white noise. The octaves occurring within the noise hold equal amounts of frequency, which result in a sound wave that has equal energy at each octave.
Pink noise can be mixed with other noises in order to create sound masking programs. For example, pink sound systems may be designed to simulate running water, a fan, or the sound of the sea. Given its soothing qualities, some people play it as background noise to help them relax. People who have sleep disorders may even purchase specialized pink sound sleep machines to help them doze off or stay sleeping throughout the night.
In particular, this noise is useful in masking low frequency sounds because it contains lower frequency levels than other types of noises. For example, pink sounds can mask noisy cars or loud industrial plants, so some employers play it in their offices to help their employees concentrate.
Pink noises have other uses as well, such as measuring the frequency response of acoustic equipment. Some synthesizers contain dedicated pink signal circuits that are used to simulate sounds like water, gunshots, wind, or explosions. Pink signals are also sometimes used when producing special effects for films, television shows, and video games. Frequently, they are used to test and equalize loudspeakers in rooms and auditoriums.