Although noise is a random signal, it can have characteristic statistical properties. Spectral density (power distribution in the frequency spectrum) is such a property, which can be used to distinguish different types of noise. This classification by spectral density is given "color" terminology, with different types named after different colors, and is common in different disciplines where noise is an important factor (like acoustics, electrical engineering and physics). Calculated spectrum of a generated approximation of white noise White noise is a random signal (or process) with a flat power spectral density. ... Pink noise spectrum Pink noise ( ), also known as 1/f noise or flicker noise, is a signal or process with a frequency spectrum such that the power spectral density is proportional to the reciprocal of the frequency. ... Brown noise spectrum In science, Brownian noise ( ), also known as Brown noise or red noise, is the kind of signal noise produced by Brownian motion. ... Wikipedia does not have an article with this exact name. ... For the Irish mythological figure, see Naoise. ... Random redirects here. ... Look up signal, signaling in Wiktionary, the free dictionary. ... In applied mathematics and physics, the spectral density is a general concept applied to a signal which may have any physical dimensions or none at all. ... In physics, power (symbol: P) is the rate at which work is performed or energy is transferred. ... Familiar concepts associated with a frequency are colors, musical notes, radio/TV channels, and even the regular rotation of the earth. ... Color is an important part of the visual arts. ... Acoustics is a branch of physics and is the study of sound (mechanical waves in gases, liquids, and solids). ... Electrical Engineers design power systems… … and complex electronic circuits. ... The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density Physics (Greek: (phúsis), nature and (phusiké), knowledge of nature) is the branch of science concerned with the discovery and characterization of universal laws which govern matter, energy, space, and time. ...

Many of these definitions assume a signal with components at all frequencies, with a spectral density per unit of bandwidth proportional to 1/f^β. For instance, white noise is flat, with β = 0, while brown has β = 2.

Technical definitions

The color names for these different types of sounds are derived from a loose analogy between the spectrum of frequencies of sound wave present in the sound (as shown in the blue diagrams) and the equivalent spectrum of light wave frequencies. That is, if the sound wave pattern of "blue noise" were translated into light waves, the resulting light would be blue, and so on.

White noise

White noise is a signal (or process) with equal energy per cycle (hertz), producing a flat frequency spectrum in linear space, named by analogy to white light.

White spectrum

In other words, the signal has equal power in any linear band, at any center frequency, having a given bandwidth. For example, the range of frequencies between 40 Hz and 60 Hz contains the same amount of power as the range between 4000 Hz and 4020 Hz has.

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 is "white" if it has a flat spectrum over a defined frequency band.

Pink spectrum

Pink noise

The frequency spectrum of pink noise is flat in logarithmic space; it has equal power in bands that are proportionally wide. This means that pink noise would have equal power in the frequency range from 40 to 60 Hz as in the band from 4000 to 6000 Hz. Since humans hear in such a proportional space, where a doubling of frequency is seen as the same size regardless of actual frequency (40–60 Hz is heard as the same interval and distance as 4000–6000 Hz), every octave contains the same amount of energy and thus pink noise is often used as a reference signal in audio engineering. That is, the human auditory system perceives approximately equal magnitude on all frequencies. The power density, compared with white noise, decreases by 3 dB per octave (density proportional to 1/f).

Brown spectrum

Brown (or red) noise

Brown noise is similar to pink noise, but with a power density decrease of 6 dB per octave with increasing frequency (density proportional to 1/f²) over a frequency range which does not include DC (in a general sense, does not include a constant component, or value at zero frequency). It can be generated by an algorithm which simulates Brownian motion or by integrating white noise. Brown noise is not named for a power spectrum that suggests the color brown; rather, the name is a corruption of Brownian motion. Also known as "random walk" or "drunkard's walk" noise.

Blue spectrum

Blue (or azure) noise

Blue noise's (FS-1037C) power density increases 3 dB per octave with increasing frequency (density proportional to f) over a finite frequency range. In computer graphics, the term "blue noise" is sometimes used more loosely as any noise with minimal low frequency components and no concentrated spikes in energy. This can be good noise for dithering (Mitchell, 1987); retinal cells are arranged in a blue-noise-like pattern for this reason (Yellot, 1983).

Purple spectrum

Purple (or violet) noise

Purple noise's power density increases 6 dB per octave with increasing frequency (density proportional to f²) over a finite frequency range. It is also known as differentiated white noise or violet noise.

Gray spectrum

Grey noise

Grey noise is random noise subjected to a psychoacoustic equal loudness curve (such as an inverted A-weighting curve) over a given range of frequencies, giving the listener the perception that it is equally loud at all frequencies.

This is in contrast to white noise, random noise which is in fact equally loud at all frequencies but not perceived as such due to the natural bias of the human ear. Calculated spectrum of a generated approximation of white noise White noise is a random signal (or process) with a flat power spectral density. ... In information theory, a signal is the sequence of states of a communications channel that encodes a message. ... Familiar concepts associated with a frequency are colors, musical notes, radio/TV channels, and even the regular rotation of the earth. ... Alternate meanings: White (disambiguation) White is a color (more accurately it contains all the colors of the spectrum and is sometimes described as an achromatic color—black is the absence of color) that has high brightness but zero hue. ... Image File history File links White_noise_spectrum. ... Image File history File links White_noise_spectrum. ... In physics, power (symbol: P) is the rate at which work is performed or energy is transferred. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... This article does not cite any references or sources. ... Image File history File links White_noise. ... Software development stages In computer programming, development stage terminology expresses how the development of a piece of software has progressed and how much further development it may require. ... Image File history File links Pink_noise_spectrum. ... Image File history File links Pink_noise_spectrum. ... Pink noise spectrum Pink noise ( ), also known as 1/f noise or flicker noise, is a signal or process with a frequency spectrum such that the power spectral density is proportional to the reciprocal of the frequency. ... A logarithmic scale is a scale of measurement that uses the logarithm of a physical quantity instead of the quantity itself. ... Audio engineering is a part of audio science dealing with the recording and reproduction of sound through mechanical and electronic means. ... In engineering, specific power (sometimes also power per unit mass or power density) refers to the amount of power delivered by an energy source, divided by some measure of the sources size or mass. ... The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power) relative to a specified or implied reference level. ... In music, an octave (sometimes abbreviated 8ve) is the interval between one musical note and another with half or double its frequency. ... Image File history File links Pink_noise. ... Software development stages In computer programming, development stage terminology expresses how the development of a piece of software has progressed and how much further development it may require. ... Image File history File links Brown_noise_spectrum. ... Image File history File links Brown_noise_spectrum. ... In science, brown noise Sample ( ♫) takes its name from Brownian motion, a random, foot-stepping pattern of motion. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... Three different views of Brownian motion, with 32 steps, 256 steps, and 2048 steps denoted by progressively lighter colors. ... In calculus, the integral of a function is an extension of the concept of a sum. ... Image File history File links Brown_noise. ... Software development stages In computer programming, development stage terminology expresses how the development of a piece of software has progressed and how much further development it may require. ... Image File history File links Blue_noise_spectrum. ... Image File history File links Blue_noise_spectrum. ... Dither is a form of noise, or erroneous signal or data which is deliberately added to sample data for the purpose of minimizing quantization error. ... Human eye cross-sectional view. ... Image File history File links Blue_noise. ... Software development stages In computer programming, development stage terminology expresses how the development of a piece of software has progressed and how much further development it may require. ... Image File history File links Purple_noise_spectrum. ... Image File history File links Purple_noise_spectrum. ... For a non-technical overview of the subject, see Calculus. ... Image File history File links Purple_noise. ... Software development stages In computer programming, development stage terminology expresses how the development of a piece of software has progressed and how much further development it may require. ... Image File history File links Gray_noise_spectrum. ... Image File history File links Gray_noise_spectrum. ...

Various noise models are employed in analysis, many of which fall under the above categories. AR noise or "autoregressive noise" is such a model, and generates simple examples of the above noise types, and more. Image File history File links Gray_noise. ... Software development stages In computer programming, development stage terminology expresses how the development of a piece of software has progressed and how much further development it may require. ... In statistics, autoregressive moving average (ARMA) models, sometimes called Box-Jenkins models after George Box and F. M. Jenkins, are typically applied to time series data. ...

The Federal Standard 1037C Telecommunications Glossary defines white, pink, blue, and black. Federal Standard 1037C, entitled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended. ...

Others

There are also many "less official" colors.

Red noise

Red noise has more than one definition:

1. A synonym for brown noise, as above [1]
2. A synonym for pink noise, as above [2]
3. Oceanic ambient noise (that is, noise from distant sources) is often described as "red" due to the selective absorption of higher frequencies by the ocean. (Common definition within the oceanographic field, contributed to a newsgroup by P.J. Rovero in 1996.) [3]

Orange noise

Orange noise is quasi-stationary noise with a finite power spectrum with a finite number of small bands of zero energy dispersed throughout a continuous spectrum. These bands of zero energy are centered about the frequencies of musical notes in whatever scale is of interest. Since all in-tune musical notes are eliminated, the remaining spectrum could be said to consist of sour, citrus, or "orange" notes.

Green noise

1. Green noise is supposedly the background noise of the world. A really long term power spectrum averaged over several outdoor sites. Rather like pink noise with a hump added around 500 Hz. [4]
2. The mid-frequency component of white noise, used in halftone dithering [5]
3. Bounded brown noise [6]

Black noise

Black noise, or silent noise, has several different definitions:

1. Silence
2. Noise with a 1/f^β spectrum, where β > 2 (Manfred Schroeder, "Fractals, chaos, power laws"). Used in modeling various environmental processes. Is said to be a characteristic of "natural and unnatural catastrophes like floods, droughts, bear markets, and various outrageous outages, such as those of electrical power." Further, "because of their black spectra, such disasters often come in clusters."
3. Noise that has a frequency spectrum of predominantly zero power level over all frequencies except for a few narrow bands or spikes. Note: An example of black noise in a facsimile transmission system is the spectrum that might be obtained when scanning a black area in which there are a few random white spots. Thus, in the time domain, a few random pulses occur while scanning. [7]
4. Whatever comes out of an active noise control system and cancels an existing noise, leaving the world noise free. The comic book character Iron Man used to have a "black light beam" that could darken a room like this, and popular sci-fi has a tendency to portray active noise control in this light.
5. As seen in the sales literature for an ultrasonic vermin repeller, black noise with a power density that is constant for a finite frequency range above 20 kHz. More accurately, ultrasonic white noise. This black noise is like the so-called black light with frequencies too high to be sensed, but still capable of affecting the environment.

Noisy white

In telecommunication, the term noisy white has the following meanings: In science, red noise, Brownian noise, or brown noise ▶(?) is the kind of signal noise produced by Brownian motion. ... Animated map exhibiting the worlds oceanic waters. ... Absorption refers to the absorption of sound waves by a material. ... In the mathematical sciences, a stationary process (or strict(ly) stationary process) is a stochastic process in which the probability density function of some random variable X does not change over time or position. ... // Music is an art form consisting of sound and silence expressed through time. ... In music, a scale is a set of musical notes that provides material for part or all of a musical work. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ... The hertz (symbol: Hz) is the SI unit of frequency. ... Left: halftone spots. ... This article or section should be merged with Dither An illustration of dithering. ... Black noise is 1. ... A fractal is a geometric object which can be divided into parts, each of which is similar to the original object. ... To meet Wikipedias quality standards, this article may require cleanup. ... Active noise control (also known as noise cancellation, active noise reduction (ANR) or antinoise) is a method for reducing unwanted sound. ... A comic book is a magazine or book containing the art form of comics. ... Iron Man (Anthony Edward Tony Stark) is a fictional comic-book superhero in the Marvel Comics universe. ... Sci-fi is an abbreviation for science fiction. ... Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz. ... Spectrum of a fluorescent black light source. ... Copy of the original phone of Alexander Graham Bell at the Musée des Arts et Métiers in Paris Telecommunication is the transmission of signals over a distance for the purpose of communication. ...

1. In facsimile or display systems, such as television, a nonuniformity in the white area of the image, i.e., document or picture, caused by the presence of noise in the received signal.
2. A signal or signal level that is supposed to represent a white area on the object, but has a noise content sufficient to cause the creation of noticeable black spots on the display surface or record medium.

Noisy black

In telecommunication, the term noisy black has the following meanings: Insert non-formatted text here For the machine that sends, receives, and produces facsimiles, see fax. ... For the Irish mythological figure, see Naoise. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ... In a communications system, the signal level is the signal power or intensity at a specified point and with respect to a specified reference level, e. ... In telecommunication, the term record medium has the following meanings: The physical medium on which information is stored in recoverable form. ... Copy of the original phone of Alexander Graham Bell at the Musée des Arts et Métiers in Paris Telecommunication is the transmission of signals over a distance for the purpose of communication. ...

1. In facsimile or display systems, such as television, a nonuniformity in the black area of the image, i.e., document or picture, caused by the presence of noise in the received signal.
2. A signal or signal level that is supposed to represent a black area on the object, but has a noise content sufficient to cause the creation of noticeable white spots on the display surface or record medium.

Insert non-formatted text here For the machine that sends, receives, and produces facsimiles, see fax. ... For the Irish mythological figure, see Naoise. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ... In a communications system, the signal level is the signal power or intensity at a specified point and with respect to a specified reference level, e. ... In telecommunication, the term record medium has the following meanings: The physical medium on which information is stored in recoverable form. ...

References

• Mitchell, Don P., "Generating Antialiased Images at Low Sampling Densities." Computer Graphics, volume 21, number 4, July 1987.
• Yellott, John I. Jr., "Spectral Consequences of Photoreceptor Sampling in the Rhesus Retina." Science, volume 221, pp. 382-385, 1983.

See also

• Mains hum - also known as the AC power hum
• Synesthesia - the psychological association of different senses, including sounds with colors

Spectrum of mains hum at 60 Hz Electric hum, mains hum, or power line hum is an audible oscillation at the frequency of the mains alternating current, which is usually 50 or 60 hertz depending on the local electric utility configuration (see Mains electricity). ... City lights viewed in a motion blurred exposure. ... Synesthesia (also spelled synæsthesia or synaesthesia, plural synesthesiae or synaesthesiae)—from the Ancient Greek (syn), meaning with, and (aisthēsis), meaning sensation—is a neurological condition in which two or more bodily senses are coupled. ...

External links

• The colors of noise newsgroup posting
• Some colored noise examples
• Rane' Pro Audio Reference definition of "noise color"
• Black Noise and Population Persistence