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Warning: Some of these seem to originate exclusively from a single newsgroup posting from October 1996 by Joseph S. Wisniewski, and should be considered questionable. The nature of the wiki will cause the definitions to converge towards the true definitions with time, making this article more accurate than the copies of that posting. Providing references for each will help with this.
This article seems to focus only on noise in terms of sound and maybe electronics. Where should something be included about noise (as a source of error) in making measurements - whether from technical or experimental source material? Of course, the same power/frequency concepts apply. Pat Heslop-Harrison 07:43, 21 May 2006 (UTC)
we could expand all of these to use the 1/fβ notation, where β = something, as used in some of these examples. — Omegatron
"The Federal Standard 1037C Telecommunications: Glossary of Telecommunication Terms defines four noise colors (white, pink, blue & black) and is considered the official source."
— Omegatron 01:45, 1 December 2005 (UTC)
Maybe it should read "Purple noise" because "Orange noise" isn't listed below. I don't know. I guess it's a matter of precision that I don't know about. Peter 03:51, 4 December 2006 (UTC)
red = brown (1/f2) definition: [5] [6]
A mean reverting stochastic process http://riskinstitute.ch/00012612.htm
A stationary and causal Gaussian first order autoregressive (AR(1)) process {Xt} with mean zero (a real oceanographic definition) http://faculty.washington.edu/dbp/PDFFILES/red-noise.pdf
Geophysical processes, for example, are often characterized by red noise backgrounds. For red noise, the variance decreases with increasing frequency. In some cases, the overall noise trend can be approximated by a first order AR model. http://www.systat.com/products/TableCurve2D/help/?sec=1080
http://www.atmos.ucla.edu/~csi/REF/pdfs/ensomjo.pdf
I have a feeling red and brown are actually the same, and red/brown is used as a model for oceanographic research. In other words, the ocean-filtered noise is not red, but is modeled by red? - Omegatron 15:54, Jun 6, 2005 (UTC)
Why put up examples that can't be played with Quicktime, Real or MS?
Most environmental noise is reddened: the variation is dominated by long-term £uctuations. Recent modelling has shown that moderately reddened noise a¡ects populations di¡erently from the white noise used in earlier studies. However, some geophysical phenomena, such as temperature and river height, can have deeply reddened `brown' or even `black' spectra http://oak.cats.ohiou.edu/~cuddingt/pubs/proceedings99.pdf
"Bounded Brownian noise" - http://www.dxarts.washington.edu/courses/565/clm-2/green.cl
"the mid-frequency component of white noise" - http://www.engr.uky.edu/~dllau/Halftone/HtmlFiles/paper2.html Used in halftone dithering
More definitions in the footnotes here: [7] — Omegatron (talk) 15:58, 12 April 2008 (UTC)
http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm
is the glossary. Each colour is in its alpahabetical place.
DavidLJ (talk) 04:54, 7 September 2013 (UTC)
So why is there supposedly a 500 Hz hump in "green noise"? Rotation of the ether? --Chinasaur 00:50, 16 Jun 2005 (UTC)
Great article, folks :-) Is anybody working on a sample of grey noise to complement the others - cause otherwise I might try to create one. Peter S. 10:20, 26 September 2005 (UTC)
I'm not a physicist and understand almost none of this, could some of it be explained or simplified somehow? Fantom 17:36, 27 November 2005 (UTC)
Doesn't the OGG encoding of the samples use psychoacoustic modelling? And wouldn't that severely distort the result, considering that grey noise is based on psychoacoustics itself? Using uncompressed or losslessly compressed sample would IMO be vastly preferable. --Brazzy 11:13, 30 November 2005 (UTC)
Now that we've got frequency graphs, it would be useful to give more significance to the layout of the page, to ensure that the graphs and their descriptions stay aligned. I'm not a Wiki or HTML expert...any takers on this? --Ktims 02:15, 14 March 2006 (UTC)
Why do you keep removing it? Its a legit WP construct is it not? Pls resond on Project Electronics as we have the same problem of organising our articles. If we dont start it soon, it will become a massive task--Light current 05:18, 5 April 2006 (UTC)
So where does shot noise fit in this scheme? I have reservations about the color-to-name scheme because I personally have heard only about white noise and pink noise (especially the uniform spectrum part). And what about Johnson noise, for that matter. What if these articles don't have a cited noise-to-color correspondence? --Ancheta Wis 20:41, 18 June 2006 (UTC)
How did this whole spectrum → color thing start, anyway? Was "white noise" coined first, to make an analogy to white light with all the colors of the spectrum present? Was "Brownian noise" coined first, named for Brownian motion, but then corrupted into a color abbreviation and followed by others? — Omegatron 17:57, 24 October 2006 (UTC)
American Heritage Dictionary just says: "[From the analogy with white light.]"
From the article:
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.
Can we get a reference on that? Brown noise, for instance, was not named for the color, and the colors listed do not actually correspond with the actual color spectrum. — Omegatron 04:37, 4 December 2006 (UTC)
The term 'DC' is not defined and I could not quickly determine its meaning via google or the disambiguation page here on wikipedia... could any help? Kinser 03:20, 18 January 2007 (UTC)
Sorry for being a party pooper, but I've removed the mains hum section. I'm sad to say, but it is not a colour, as the title of the article tells me, and there is an article named Mains hum. Also, it isn't a pure noise (i.e., it isn't "a random signal", as the first paragraph of the article says), I hope everyone is okay with that. I'll move the relevant discussion to Talk:Mains hum now. +mwtoews 08:50, 8 February 2007 (UTC)
Funny as some people may have found it, I have removed the comment about orange noise being generated by a class of first graders on plastic recorders. It was a dumb joke, insulting to a real musical instrument, and factually incorrect. Thee strikes and that comment is out. —The preceding unsigned comment was added by Eijkhout (talk • contribs) 13:51, 18 February 2007 (UTC).
i thought colors of noise were used to differentiate between levels of structured or erratic noise. did i believe another ghost then?· Lygophile has spoken 17:18, 19 March 2007 (UTC)
Sorry if I'm being dumb here, but I'm struggling to understand how the graphs, particularly of white v pink noise, relate to their descriptions. White noise is described as having a flat frequency spectrum in linear space, but the graph shows a (roughly) flat spectrum with a logarithmic scale. Pink noise is described as being "flat in logarithmic space", but its graph shows a downward trend on the same log scale. I'm guessing that the y-axis of the graphs (dB) is not what they are "flat" in (ie power?), but it all seems horribly confusing. Also the slight rise in the white noise graph is attributed to it being a log rather than linear scale, but that can't be right, if it were on a linear scale it would surely slope downwards dramatically -- so it seems more like the slight rise is an aberration and this isn't true white noise (hardly surprising if it was generated from an OGG file...) Can anyone shed some light? Thanks. 217.169.15.38 19:23, 11 October 2007 (UTC)
The y axis of the graphs is logarithmic. dB are logarithmic. Maybe it would be better to have two axes, one log (1, 10, 100, 1000) and the opposing axis in dB, to make this clear.
The x axis is logarithmic, but the measurement is from an FFT, so the measurement bin divisions are linear. I see how this could be confusing, but the angled straight line spectrums will not show up unless they are plotted on a log-log plot.
Hmm... The slight rise in the white noise appears in Adobe Audition, too, which I think was performed on the original wave file. Could be an artifact of Audition's white noise generator (aliasing?), an artifact of the measurement method, or an artifact of the way it's plotted.
Also, is the grey noise completely wrong? I used white noise and filtered it with an inverted A-weighting curve. But maybe it should have started with pink noise?
It would be better if both the signals and the analysis were generated purely in mathematics software (GNU Octave), rather than audio software, but I never got around to this. — Omegatron (talk) 15:38, 12 April 2008 (UTC)
In some aspects sound and light are not even considered to have any relationship, but in some cases the two phenomena can be represented with similar models. An example of the latter case is that a sampling in the time domain of the respective field variables of the both phenomena could be Fourier transformed to the frequency domain and be represented as (e.g.) energy distribution vs frequency. Since different distributions of light energy vs frequency can be interpreted as different colours (which is a very obvious interpretation), it is very tempting to do an analogy with sound. But, since sound and light are perceived totally different, it does not make much sense to do a translation of colours to sounds, apart from in some (actually very few) cases:
Evenly distributed noise (in a linear sense, i.e. perfectly random noise) can be called white and the logarithmically distributed counterpart can be called pink in order to suggest that the energy in the low frequency region is dominating in the latter case. The same line of reasoning can be applied for blue light/noise (a domination of high frequency contents) and for black light/noise (absense of energy throughout the whole frequency range, which does not seem as much of a "help" for visualising the nature of the noise - it is kind of obvious anyway). These definitions can be seen as "standard" definitions, are more or less well-established and give a good picture of how the noise is distributed in each case.
But when it comes to the other colours than these mentioned it is not possible to make an obvious and unique interpretation. Neither will these interpretation be of any help. In the best of scenarios we have some academic interpretations that will not help by giving any "feeling" of what kind of noise it is. A nonsense name would be equally sufficient. In the worst scenario we have some childish and far-fetched attempts to make analogies that are both misleading and non-intuitive.
For example: Brown noise is not even an analogy to the corresponding colour. Furthermore, if brown noise is considered as a result of Brownian motion, then the energy distribution is a result of how you implement the random walk amplitude and frequency wise. The resulting distribution can be totally different from what is stated here (the definition here is as meaningful as claiming that the top speed of a car is twice the top speed of a bus). Also the usefulness of such noise can be doubted. Nevertheless, this definition has some merits, mostly because it has been around for some time. Red noise actually implies absence of high frequency contents (dark pink had been more appropriate...) Purple noise is maybe relevant, but it should in that case replace the blue noise definition, which in analogy to the pink noise actually should be called light blue... The grey noise definition contradicts the notion of white noise being perceived as white. Furthermore, its energy distribution should, according to how it is defined here, be a function of the absolute sound pressure level. It will therefore be meaningless nonsense in a file, as a electrical signal and so on unless it is played back at a corresponding calibrated level. These colours, plus orange, green and so on, are all more or less unnecessary constrained constructions.
Thus, if there is no motive to invent new non-standard noise-colour analogies: Please refrain from creating or promoting personal home-made definitions! It only gives too much importance to an analogy which is not inuitive - does anyone really think there is a common notion of, for example, how "green" would sound? –– DrD 22:29, 9 November 2007 (UTC)
I started the process of re-generating all the noise audio samples from scratch in GNU Octave. So far I've just got Image:White noise.ogg (uniformly distributed) and Image:Gaussian white noise.ogg (normally distributed).
The Gaussian file sounds about 4.5 dB quieter than the uniformly-distributed file, while SoX says they are actually 8.4 dB different. Is this psychoacoustics or did I measure something wrong? — Omegatron (talk) 04:58, 21 April 2008 (UTC)
^ a b c d e Joseph S. Wisniewski (07 Oct 1996). "Colors of noise pseudo FAQ, version 1.3". comp.dsp. (Web link). Retrieved on 2008-05-04.
The above reference links to an email address...Dbutler1986 (talk) 00:21, 16 July 2008 (UTC)
It would be nice if the article explained what this is all about. Sincerely, GeorgeLouis (talk) 07:08, 24 July 2008 (UTC)
White audio noise sounds like a high-frequency hiss; white image noise looks like static and can perceptually be removed with a low-pass filter. Could someone explain the difference between the definition of white noise and this intuitive sense that white noise is a high-frequency noise? I assume it has to do with the difference between energy and amplitude of a frequency band and that blue or violet noise would be perceptually uniform across the spectrum (and so wouldn't be removed easily by a low-pass filter). —Ben FrantzDale (talk) 15:18, 15 September 2008 (UTC)
"red noise" has ended up linked from a cliamte page. But the defn here is far far too specific. "red noise" (no-one uses brown) from the climate point of view is just noise with more power at lower frequencies. None of this 6-db-per-whatever stuff William M. Connolley (talk) 21:02, 16 September 2008 (UTC)
I'm not questioning whether the entirety of the "black noise" description is a joke, just a part of it. The article says:
and cites Manfred Schroeder's book _Fractals, chaos, power laws_. I don't have this book and Amazon won't let me search it. Basically I'm wondering if this description is some kind of joke about power outages during natural disasters.
-- Theclapp (talk) 22:09, 6 January 2009 (UTC)
Binksternet (talk · contribs) reverted my edit: (rv source takes unique liberties with language, not notable) It cited a book written by Tricia Rose, who appears notable enough to have an article about her, and a CD of random numbers by George Marsaglia, who appears notable enough to have an article about him. Is the book Black Noise (ISBN 9780819562753) "not notable"? Or is the Marsaglia Random Number CD-ROM "not notable"? --Damian Yerrick (talk | stalk) 03:06, 17 August 2011 (UTC)
Would it be ok to remove the silly batman references in an otherwise perfectly ok article? 94.208.253.113 (talk) 19:44, 4 February 2013 (UTC)
Seeking comments before I strike this sentence:
Electricmic (talk) 09:05, 3 November 2009 (UTC)
What noise is heard on FM radio tuned to clear frequency? —Preceding unsigned comment added by Boskoigic (talk • contribs) 19:36, 3 February 2010 (UTC)
I think the article should explain not only what are the colours of noise but also the implications. You often hear physicists referring to different colours of noise so IMHO an explanation of the implications would be useful.
It must be noted that the spectrum (FFT output, dB, amplitudes) and the spectral density has different units and thus also noise slopes. Pink noise figure - in dB (not in dB/rootHz) but the spectral density stated. White noise - flat spectrum (not spectral density) - http://www.1w.net/nyu/wnoise.html . This article must be rewritten!
brown noise can refer to noise that is a frequency that moves the bowels, this should be under unofficial colours 188.223.18.19 (talk) 19:25, 17 March 2012 (UTC)
As a general rule, the name of a Wikipedia article should be a singular noun. E.g. the article about pigs is called "Pig" rather than "Pigs", even though it talks about all the billion pigs in the world and all the umpteen breeds of pigs. That rule is useful for readers and editors alike, since it helps them guess the right name of the article. So this article should preferably be renamed "Color of noise" or "Noise color", without changing its contents. --Jorge Stolfi (talk) 02:36, 13 March 2013 (UTC)
The colours of third-octave noises are missing in this article. These are frequently used for audio analysis. See also: Third-Octave Filter Banks --Bautsch (talk) 12:46, 30 October 2013 (UTC)
"Pink noise is the only power-law spectral density that has this property: all steeper power-law spectra are finite if integrated to the high-frequency end, and all flatter power-law spectra are finite if integrated to the DC, low-frequency limit."
Wouldn't this apply to blue noise, too? — Preceding unsigned comment added by 96.224.69.35 (talk) 15:00, 22 May 2014 (UTC)
No, in that case the integral is clearly diverging. pink noises is the integral of 1/f df, which is log, which is -inf at zero and inf at inf. blue noise is int f df, which is f^2, inf at inf and zero at zero. — Preceding unsigned comment added by 100.45.64.131 (talk) 04:44, 17 July 2014 (UTC)
What kind of bounds are meant to be applied? Most likely the process should be bounded in the space or amplitude domain (i.e., the position of the particle undergoing Brownian motion is constrained within some "container"), but another definition of green noise mentions bounding of white noise in the frequency domain, so I want to make sure.
I noticed that this is the only green-noise definition that currently lacks a citation. A previous discussion on this talk page mentioned http://www.dxarts.washington.edu/courses/565/clm-2/green.cl, but that looks like a dead link (returns HTTP 200 after redirecting to the domain without www, but "There are no courses listed on our site that meet your filtering criteria."). --SoledadKabocha (talk) 20:42, 13 September 2015 (UTC) (+proofread by self 04:50, 19 October 2015 (UTC))
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It should give examples of noises by color that people commonly hear in everyday life. PlanetStar 19:16, 6 October 2017 (UTC)
The introductory paragraph gives an overview with mentions of "power" and "power spectrum", with those terms linking to their corresponding Wikipedia entries. However, these entries are generic explanations of these terms as used in physics and engineering, and not helpful in understanding how they are applied to sound, and specifically to noise color. Each subsequent technical definition for specific colors of noise refer to the power for each frequency band but it is still a mystery to the layman, even a reasonably well-informed layman, exactly what is meant by "power" here. A layman's explanation of this term specific to the topic of noise color would be much appreciated. — Preceding unsigned comment added by 6StringJazzer (talk • contribs) 15:24, 2 December 2018 (UTC)
Quantum fluctuations of the electromagnetic field in the vacuum are blue noise, are they not? (3D blue noise power being proportional to f^3, just like 3D pink noise is proportional to f^-3). This should be added. 97.116.77.170 (talk) 19:38, 11 August 2019 (UTC)
For example, the description of white noise makes you expect either a graph in logarithmic frequency space that slopes up as the frequency increases, or a graph in linear frequency space that stays flat. Currently it has a graph in logarithmic frequency space where the power stays flat, which seems wrong, but many commercial music production spectrometers graph white noise similarly, so it can't be completely wrong.
I wonder if the difference between these methods is measuring the power of single frequencies along the spectrum which leads to a flat graph regardless of the type of frequency space, versus measuring the average power of ranges of frequencies that correspond to equal width sections in the graph, which would lead to a sloped graph in logarithmic space. :shrug: 80.220.73.154 (talk) 00:52, 29 January 2020 (UTC)
To my understanding Brownian noise is not the same as red or brown noise: Brownian noise has memory, like the random walk of moving molecules, and is normal-distributed. While red and brown noise don't have memory, - they are the result of filtered equal distributed white noise. The confusion might happen because for experiments mostly the spectral density is the only importance, together with the similar naming. 93.237.16.85 (talk) 23:43, 11 April 2022 (UTC)
There are some legit sound deisgn co. that points towards an existence of Green and Orange Noise. See https://emastered.com/blog/different-types-of-noise 183.179.53.41 (talk) 07:08, 24 August 2022 (UTC)