Editing Decibel (section)

== History ==
The decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. Until the mid-1920s, the unit for loss was ''miles of standard cable'' (MSC). 1&nbsp;MSC corresponded to the loss of power over one [[mile]] (approximately 1.6&nbsp;km) of standard telephone cable at a frequency of {{val|5000}}&nbsp;[[radian]]s per second (795.8&nbsp;Hz), and matched closely the smallest attenuation detectable to a listener. A standard telephone cable was "a cable having uniformly distributed resistance of 88&nbsp;ohms per loop-mile and uniformly distributed [[shunt (electrical)|shunt]] [[capacitance]] of 0.054&nbsp;[[microfarad]]s per mile" (approximately corresponding to 19&nbsp;[[wire gauge|gauge]] wire).<ref>{{cite book |last=Johnson |first=Kenneth Simonds |title=Transmission Circuits for Telephonic Communication: Methods of analysis and design |date=1944 |publisher=[[D. Van Nostrand Co.]] |location=New York |page=10}}</ref>

In 1924, [[Bell Labs|Bell Telephone Laboratories]] received a favorable response to a new unit definition among members of the International Advisory Committee on Long Distance Telephony in Europe and replaced the MSC with the ''Transmission Unit'' (TU). 1&nbsp;TU was defined such that the number of TUs was ten times the base-10 logarithm of the ratio of measured power to a reference power.<ref>{{cite book |title=Sound system engineering |edition=2nd |author-first1=Don |author-last1=Davis |author-first2=Carolyn |author-last2=Davis |publisher=[[Focal Press]] |date=1997 |isbn=978-0-240-80305-0 |page=35 |url={{Google books|plainurl=yes|id=9mAUp5IC5AMC|page=35}}}}</ref>
The definition was conveniently chosen such that 1&nbsp;TU approximated 1&nbsp;MSC; specifically, 1&nbsp;MSC was 1.056&nbsp;TU. In 1928, the Bell system renamed the TU into the decibel,<ref>{{cite journal |journal=Bell Laboratories Record |title='TU' becomes 'Decibel' |author-first=R. V. L. |author-last=Hartley |author-link=R. V. L. Hartley |volume=7 |issue=4 |publisher=AT&T |pages=137–139 |date=December 1928 |url={{Google books|plainurl=yes|id=h1ciAQAAIAAJ}}}}</ref> being one tenth of a newly defined unit for the base-10 logarithm of the power ratio. It was named the ''bel'', in honor of the telecommunications pioneer [[Alexander Graham Bell]].<ref>{{Cite journal |author-last=Martin |author-first=W. H. |date=January 1929 |title=DeciBel—The New Name for the Transmission Unit |journal=[[Bell System Technical Journal]] |volume=8 |issue=1}}</ref>
The bel is seldom used, as the decibel was the proposed working unit.<ref>{{Google books |id=EaVSbjsaBfMC |page=276 |title=100 Years of Telephone Switching}}, Robert J. Chapuis, Amos E. Joel, 2003</ref>

The naming and early definition of the decibel is described in the [[National Institute of Standards and Technology|NBS]] Standard's Yearbook of 1931:<ref>{{Cite journal |title=Standards for Transmission of Speech |journal=Standards Yearbook |volume=119 |author-first=William H. |author-last=Harrison |date=1931 |publisher=National Bureau of Standards, U. S. Govt. Printing Office}}</ref>

{{blockquote |
Since the earliest days of the telephone, the need for a unit in which to measure the transmission efficiency of telephone facilities has been recognized. The introduction of cable in 1896 afforded a stable basis for a convenient unit and the "mile of standard" cable came into general use shortly thereafter. This unit was employed up to 1923 when a new unit was adopted as being more suitable for modern telephone work. The new transmission unit is widely used among the foreign telephone organizations and recently it was termed the "decibel" at the suggestion of the International Advisory Committee on Long Distance Telephony.

The decibel may be defined by the statement that two amounts of power differ by 1 decibel when they are in the ratio of 10<sup>0.1</sup> and any two amounts of power differ by ''N'' decibels when they are in the ratio of 10<sup>''N''(0.1)</sup>. The number of transmission units expressing the ratio of any two powers is therefore ten times the common logarithm of that ratio. This method of designating the gain or loss of power in telephone circuits permits direct addition or subtraction of the units expressing the efficiency of different parts of the circuit&nbsp;...}}

{{anchor|Logit}}In 1954, J. W. Horton argued that the use of the decibel as a unit for quantities other than transmission loss led to confusion, and suggested the name ''logit'' for "standard magnitudes which combine by multiplication", to contrast with the name ''unit'' for "standard magnitudes which combine by addition".<ref>{{cite journal |first=J. W. |last=Horton |title=The bewildering decibel |journal=Electrical Engineering |volume=73 |issue=6 |pages=550–555 |year=1954|doi=10.1109/EE.1954.6438830 |s2cid=51654766 }}
</ref>{{clarify|date=March 2018}}

In April&nbsp;2003, the [[International Committee for Weights and Measures]] (CIPM) considered a recommendation for the inclusion of the decibel in the [[International System of Units]] (SI), but decided against the proposal.<ref>{{cite web |url=http://www.bipm.org/utils/common/pdf/CC/CCU/CCU16.pdf |archive-url=https://web.archive.org/web/20141006105908/http://www.bipm.org/utils/common/pdf/CC/CCU/CCU16.pdf |archive-date=2014-10-06 |url-status=live |publisher=Consultative Committee for Units |title=Meeting minutes |at=Section 3}}</ref> However, the decibel is recognized by other international bodies such as the [[International Electrotechnical Commission]] (IEC) and [[International Organization for Standardization]]  (ISO).<ref name="IEC60027-3">{{cite web |url=http://webstore.iec.ch/webstore/webstore.nsf/artnum/028981 |title=Letter symbols to be used in electrical technology |at=Part 3: Logarithmic and related quantities, and their units |id=IEC&nbsp;60027-3, Ed.&nbsp;3.0 |publisher=International Electrotechnical Commission |date=19 July 2002}}</ref> The IEC permits the use of the decibel with root-power quantities as well as power and this recommendation is followed by many national standards bodies, such as [[NIST]], which justifies the use of the decibel for [[voltage]] ratios.<ref name="NIST2008"/>  In spite of their widespread use, [[#Suffixes and reference values|suffixes]] (such as in [[A-weighting|dBA]] or dBV) are not recognized by the IEC or ISO.