Editing Colors of noise (section)

===Violet noise===
[[Image:Violet noise spectrum.svg|thumb|right|Violet spectrum (+6.02&nbsp;dB/octave)]]

Violet noise is also called '''purple noise'''. Violet noise's power density increases 6.02&nbsp;dB per octave with increasing frequency<ref>Transactions of the American Society of Heating, Refrigerating and Air-Conditioning Engineers 1968 [https://books.google.com/books?doi=aTJSAAAAMAAJ&q=%22purple+noise%22] Quote: 'A "purple noise," accordingly, is a noise the spectrum level of which ''rises'' with frequency.'</ref><ref>{{cite conference | doi=10.1109/PLANS.1996.509090 | first1=Q. J. | last1=Zhang | first2=K.-P. | last2=Schwarz | title=Estimating double difference GPS multipath under kinematic conditions| book-title=Proceedings of the Position Location and Navigation Symposium – PLANS '96 | publisher=[[IEEE]] | location= Atlanta, GA, USA | conference = Position Location and Navigation Symposium – PLANS '96 |pages=285–91 | date = April 1996}}</ref> "The spectral analysis shows that GPS acceleration errors seem to be violet noise processes. They are dominated by high-frequency noise." (density proportional to ''f''&nbsp;<sup>2</sup>) over a finite frequency range. It is also known as [[Derivative|differentiated]] white noise, due to its being the result of the differentiation of a white noise signal.

Due to the diminished sensitivity of the human ear to high-frequency hiss and the ease with which white noise can be electronically differentiated (high-pass filtered at first order), many early adaptations of dither to digital audio used violet noise as the dither signal.{{Citation needed|date=March 2020}}

Acoustic thermal noise of water has a violet spectrum, causing it to dominate [[hydrophone]] measurements at high frequencies.<ref name="Hildebrand2009">{{cite journal | doi=10.3354/meps08353 | title=Anthropogenic and natural sources of ambient noise in the ocean | date=2009 | first1=John A. | last1=Hildebrand | pages = 478–480 | journal=Marine Ecology Progress Series| volume=395 | bibcode=2009MEPS..395....5H | doi-access=free }}</ref> "Predictions of the thermal noise spectrum, derived from classical statistical mechanics, suggest increasing noise with frequency with a positive slope of 6.02&nbsp;dB octave<sup>−1</sup>." "Note that thermal noise increases at the rate of 20&nbsp;dB decade<sup>−1</sup>"<ref>{{cite journal | last1 = Mellen | first1 = R. H. | date=1952 | title= The Thermal-Noise Limit in the Detection of Underwater Acoustic Signals | journal = The Journal of the Acoustical Society of America | volume = 24 | issue=5 | pages = 478–80 | doi=10.1121/1.1906924| bibcode = 1952ASAJ...24..478M }}</ref>

{{Listen|filename=Purple noise.ogg|title=10 seconds of violet noise|description=}}
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