Neper: Difference between revisions
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{{main|Level (logarithmic quantity)}} | {{main|Level (logarithmic quantity)}} | ||
The neper is defined in terms of ratios of field quantities — also called ''root-power quantities'' — (for example, [[voltage]] or [[Current (electricity)|current]] amplitudes in electrical circuits, or [[sound pressure|pressure]] in [[acoustics]]), whereas the decibel was originally defined in terms of [[power (physics)|power]] ratios. A power ratio 10 log ''r'' dB is equivalent to a field-quantity ratio 20 log ''r'' dB, since power in a linear system is proportional to the square ([[Joule's first law|Joule's laws]]) of the amplitude. Hence the decibel and the neper have a fixed ratio to each other:<ref>{{cite journal |date=January 2022 |orig-date=2021-11-09 |title=A terminology standard for underwater acoustics and the benefits of international standardization. | The neper is defined in terms of ratios of field quantities — also called ''root-power quantities'' — (for example, [[voltage]] or [[Current (electricity)|current]] amplitudes in electrical circuits, or [[sound pressure|pressure]] in [[acoustics]]), whereas the decibel was originally defined in terms of [[power (physics)|power]] ratios. A power ratio 10 log ''r'' dB is equivalent to a field-quantity ratio 20 log ''r'' dB, since power in a linear system is proportional to the square ([[Joule's first law|Joule's laws]]) of the amplitude. Hence the decibel and the neper have a fixed ratio to each other:<ref>{{cite journal |date=January 2022 |orig-date=2021-11-09 |title=A terminology standard for underwater acoustics and the benefits of international standardization. |journal=[[IEEE Journal of Oceanic Engineering]] |publisher=[[IEEE]] |volume=47 |issue=1 |pages=179-200 [Appendix B Decibel: Past, Present, and Future – Section D] |doi=10.1109/JOE.2021.3085947 |issn=0364-9059 |eissn=1558-1691 |s2cid=243948953 |doi-access=free |author-last1=Ainslie |author-first1=Michael A. |author-last2=Halvorsen |author-first2=Michele B. |author-last3=Robinson |author-first3=Stephen P. |bibcode=2022IJOE...47..179A }} [https://web.archive.org/web/20221220112042/https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=9607022] (22 pages)</ref> | ||
:<math> 1\ \text{Np} = 20 \log_{10} e\ \text{dB} \approx \text{8.685889638 dB} </math> | :<math> 1\ \text{Np} = 20 \log_{10} e\ \text{dB} \approx \text{8.685889638 dB} </math> | ||
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The neper is a natural linear unit of [[relative difference]], meaning in nepers (logarithmic units) relative differences add rather than multiply. This property is shared with logarithmic units in other bases, such as the bel. | The neper is a natural linear unit of [[relative difference]], meaning in nepers (logarithmic units) relative differences add rather than multiply. This property is shared with logarithmic units in other bases, such as the bel. | ||
The derived units decineper (1 dNp = 0.1 neper) and '''centineper''' (1 cNp = 0.01 neper) are also used.<ref>{{cite book |title=Glossary of Telecommunication Terms |date=1980 |publisher=General Services Administration, Federal Supply Service |page=73 |url=https://books.google.com/books?id=3cQ65jxbaTAC&pg=PA73 |language=en}}</ref> The centineper for root-power quantities corresponds to a [[log point]] or log percentage, see ''{{section link|Relative change and difference#Logarithmic scale}}''.<ref name="Blythe2020">{{cite journal |last1=Karjus |first1=Andres |last2=Blythe |first2=Richard A. |last3=Kirby |first3=Simon |last4=Smith |first4=Kenny |title=Quantifying the dynamics of topical fluctuations in language |journal=Language Dynamics and Change |date=10 February 2020 |volume=10 |issue=1 |pages=86–125 |doi=10.1163/22105832-01001200 |s2cid=46928080 | The derived units decineper (1 dNp = 0.1 neper) and '''centineper''' (1 cNp = 0.01 neper) are also used.<ref>{{cite book |title=Glossary of Telecommunication Terms |date=1980 |publisher=General Services Administration, Federal Supply Service |page=73 |url=https://books.google.com/books?id=3cQ65jxbaTAC&pg=PA73 |language=en}}</ref> The centineper for root-power quantities corresponds to a [[log point]] or log percentage, see ''{{section link|Relative change and difference#Logarithmic scale}}''.<ref name="Blythe2020">{{cite journal |last1=Karjus |first1=Andres |last2=Blythe |first2=Richard A. |last3=Kirby |first3=Simon |last4=Smith |first4=Kenny |title=Quantifying the dynamics of topical fluctuations in language |journal=Language Dynamics and Change |date=10 February 2020 |volume=10 |issue=1 |pages=86–125 |doi=10.1163/22105832-01001200 |s2cid=46928080 |doi-access=free |arxiv=1806.00699 }}</ref> | ||
== See also == | == See also == | ||
Latest revision as of 08:36, 9 November 2025
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The neper (symbol: Np) is a logarithmic unit for ratios of measurements of physical field and power quantities, such as gain and loss of electronic signals. The unit's name is derived from the name of John Napier, the inventor of logarithms. As is the case for the decibel and bel, the neper is a unit defined in the international standard ISO 80000. It is not part of the International System of Units (SI), but is accepted for use alongside the SI.[1]
Definition
Like the decibel, the neper is a unit in a logarithmic scale. While the bel uses the decadic (base-10) logarithm to compute ratios, the neper uses the natural logarithm, based on Euler's number (e ≈ 2.71828). The level of a ratio of two signal amplitudes or root-power quantities, with the unit neper, is given by[2]
where and are the signal amplitudes, and lnScript error: No such module "Check for unknown parameters". is the natural logarithm. The level of a ratio of two power quantities, with the unit neper, is given by[2]
where and are the signal powers.
In the International System of Quantities, the neper is defined as 1 Np = 1.[3]
Units
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The neper is defined in terms of ratios of field quantities — also called root-power quantities — (for example, voltage or current amplitudes in electrical circuits, or pressure in acoustics), whereas the decibel was originally defined in terms of power ratios. A power ratio 10 log r dB is equivalent to a field-quantity ratio 20 log r dB, since power in a linear system is proportional to the square (Joule's laws) of the amplitude. Hence the decibel and the neper have a fixed ratio to each other:[4]
and
The (voltage) level ratio is
Like the decibel, the neper is a dimensionless unit. The International Telecommunication Union (ITU) recognizes both units. Only the neper is coherent with the SI.[5]
Applications
The neper is a natural linear unit of relative difference, meaning in nepers (logarithmic units) relative differences add rather than multiply. This property is shared with logarithmic units in other bases, such as the bel.
The derived units decineper (1 dNp = 0.1 neper) and centineper (1 cNp = 0.01 neper) are also used.[6] The centineper for root-power quantities corresponds to a log point or log percentage, see Template:Section link.[7]
See also
References
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- ↑ Script error: No such module "Citation/CS1". [1] (22 pages)
- ↑ ISO 80000-3:2007 §0.5
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Works
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Further reading
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