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This article is about white noise as a scientific concept, see also:
White noise is a signal (or process) with a flat frequency spectrum. In other words, the signal has equal power in any band, at any centre frequency, having a given bandwidth.
An infinite-bandwidth white noise signal is purely a theoretical construct. By having power at all frequencies, the total power of such a signal would be infinite. In practice a signal can be "white" with a flat spectrum over a defined frequency band.
A signal that is "white" in the frequency domain must have certain important statistical properties in time. For example, it must have zero autocorrelation with itself over time, except at zero timeshift. Conversely, if the autocorrelation of a signal has those properties (zero except at zero timeshift), the signal is white.
Being uncorrelated in time does not however restrict the values a signal can take. Any distribution of values is possible (although it must have zero DC component). For example, a binary signal which can only take on the values +1 or -1 will be white if the sequence of zeros and ones is statistically uncorrelated. Noise having a continuous distribution, such as a normal distribution, can of course be white.
It is often incorrectly assumed that Gaussian noise (see normal distribution) is necessarily white noise. However, neither property implies the other. Thus, the two words "Gaussian" and "white" are often both specified in mathematical models of systems. Gaussian white noise is a good approximation of many real-world situations and generates mathematically tractable models.
There are other forms of noise with various frequency characteristics that are classified by "color".
The next most commonly used color is pink noise. Its frequency spectrum is not flat, but has equal power in octave bands. Pink noise is perceptually white. That is, the human auditory system perceives equal magnitude on all frequencies. The power density decreases by -3 dB per octave (density proportional to 1/f).
Brown noise is similar to pink noise, but with a decrease of -6 dB per octave power density (density proportional to 1/f2). It can be generated by an algorithm which simulates Brownian motion.There are also many "less official" colors.
One use for white noise is in the field of architectural acoustics. Here in order to submerge distracting, undesirable noises (for example conversations, etc.,) in interior spaces, a constant low level of noise is generated and provided as a background sound.
White noise has also been used in electronic musicElectronic music is a loose term for music created using electronic equipment. Any sound produced by the means of an electrical signal may reasonably be called electronic, and the term is sometimes used that way in music where acoustic performance is the, where is it used either directly or as an input for a filter to create other types of noise signal.
To set up the EQEQ can mean: Education Quotient, a measure of education quality EverQuest a multiplayer computer role-playing game Equalization in audio processing Emotional Quotient in how a person handles emotional stress Lists of two-letter combinations. for a concert or other perfomance in a venue, white noise is sent through the PA system and monitored from various points in the venue so that the engineer can tell if the acoustics of the building naturally boost or cut any frequencies and can compensate with the mixer.