Editing Decibel (section)

=== Voltage ===
Since the decibel is defined with respect to power, not amplitude, conversions of voltage ratios to decibels must square the amplitude, or use the factor of 20 instead of 10, as discussed above.

[[File:Relationship between dBu and dBm.png|thumb|upright=1.25|A schematic showing the relationship between [[dBu|dB{{sub| u}}]] (the [[voltage source]]) and dB{{sub| m}} (the power dissipated as [[heat]] by the 600&nbsp;Ω [[resistor]])]]

; dB{{sub| V}} : dB(V<sub>[[root mean square|RMS]]</sub>)&nbsp;– voltage relative to 1&nbsp;volt, regardless of impedance.<ref name=clqgmk>{{cite web |title=V<sub>RMS</sub> / dBm / dBu / dBV calculator |department=Utilities |publisher=Analog Devices |url=http://designtools.analog.com/dt/dbconvert/dbconvert.html |via=designtools.analog.com |access-date=2016-09-16}}</ref> This is used to measure microphone sensitivity, and also to specify the consumer [[Line level|line-level]] of {{nowrap|−10 dBV}}, in order to reduce manufacturing costs relative to equipment using a {{nowrap|+4 dBu}} line-level signal.<ref>{{cite book |last=Winer |first=Ethan |year=2013 |title=The Audio Expert: Everything you need to know about audio |publisher=Focal Press |isbn=978-0-240-82100-9 |page=[https://books.google.com/books?id=TIfOAwAAQBAJ&q=%22%E2%88%9210+dBV%22+%221+kHz%22 107] |url=https://books.google.com/books?id=TIfOAwAAQBAJ |via=Google }}</ref>

; dB{{sub| u}} or dB{{sub| v}} : RMS voltage relative to {{nowrap|<math>V = \sqrt{600\ \Omega\ \cdot\ 0.001\ \mathsf{W}\;} \approx 0.7746\ \mathsf{V}\ </math>}} (i.e. the voltage that would dissipate 1&nbsp;mW into a 600&nbsp;Ω load). An RMS voltage of 1&nbsp;V therefore corresponds to <math>\ 20\cdot\log_{10} \left( \frac{\ 1\ V_\mathsf{RMS}\ }{ \sqrt{0.6\ }\ V} \right) = 2.218\ \mathsf{dB_u} ~.</math><ref name=clqgmk/> Originally dB{{sub| v }}, it was changed to dB{{sub| u}} to avoid confusion with dB{{sub| V}}.<ref>{{cite web |first=Stas |last=Bekman  |title=3.3 – What is the difference between dBv, dBu, dBV, dBm, dB&nbsp;SPL, and plain old dB? Why not just use regular voltage and power measurements? |website=stason.org |department=Entertainment audio |series=TULARC |url=http://stason.org/TULARC/entertainment/audio/pro/3-3-What-is-the-difference-between-dBv-dBu-dBV-dBm-dB.html }}</ref> The ''v'' comes from ''volt'', while ''u'' comes from the [[volume unit|volume ''unit'']] displayed on a [[VU meter]].<ref>{{cite AV media |first=Rupert |last=Neve |author-link=Rupert Neve |date=9 October 2015 |title=Creation of the dB{{sub| u}} standard level reference |medium=video |url=https://www.youtube.com/watch?v=b02P4f3CBuM | archive-url=https://ghostarchive.org/varchive/youtube/20211030/b02P4f3CBuM |archive-date=2021-10-30 }}{{cbignore}}</ref>{{paragraphbreak}}dB{{sub| u}} can be used as a measure of voltage, regardless of impedance, but is derived from a 600&nbsp;Ω load dissipating 0&nbsp;dB{{sub| m}} (1&nbsp;mW). The reference voltage comes from the computation <math>\ 7 \mathsf{V} = \sqrt{R \cdot P\ }\ </math> where <math>\ R\ </math> is the resistance and <math>\ P\ </math> is the power.

: In [[professional audio]], equipment may be calibrated to indicate a "0" on the VU meters some finite time after a signal has been applied at an amplitude of {{nobr|+4 dBu}}. Consumer equipment typically uses a lower "nominal" signal level of {{nobr|−10 dB{{sub| V}} .}}<ref>{{cite web |title=dB or not dB&nbsp;? |website=deltamedia.com |url=http://www.deltamedia.com/resource/db_or_not_db.html |url-status=dead |access-date=2013-09-16 |archive-url=https://web.archive.org/web/20130620064637/http://www.deltamedia.com/resource/db_or_not_db.html |archive-date=20 June 2013 }}</ref> Therefore, many devices offer dual voltage operation (with different gain or "trim" settings) for interoperability reasons. A switch or adjustment that covers at least the range between {{nobr|+4 dB{{sub| u}}}} and {{nobr|−10 dB{{sub| V}}}} is common in professional equipment.

; dB{{sub| m0s}} : Defined by Recommendation ITU-R V.574&nbsp;; dB{{sub| mV}}: dB(mV<sub>RMS</sub>) – root mean square voltage relative to 1&nbsp;millivolt across 75&nbsp;Ω.<ref>
{{cite book
 |title=The IEEE Standard Dictionary of Electrical and Electronics terms
 |edition=6th
 |year=1996
 |orig-year=1941
 |publisher=[[Institute of Electrical and Electronics Engineers]]
 |isbn=978-1-55937-833-8
}}
</ref> Widely used in [[cable television]] networks, where the nominal strength of a single TV signal at the receiver terminals is about 0&nbsp;dB{{sub| mV}}. Cable&nbsp;TV uses 75&nbsp;Ω coaxial cable, so 0&nbsp;dB{{sub| mV}} corresponds to −78.75&nbsp;dB{{sub| W}} {{nobr|( −48.75 dB{{sub| m}} )}} or approximately 13&nbsp;nW.

; dB{{sub| μV}} or dB{{sub| uV}} : dB(μV<sub>RMS</sub>) – voltage relative to 1&nbsp;microvolt. Widely used in television and aerial amplifier specifications. 60&nbsp;dBμV&nbsp;= 0&nbsp;dB{{sub| mV}}.