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<p><b>New page</b></p><div>[[File:Relationship_between_dBu_and_dBm.png|thumb|Relationship_between_dBu_and_dBm.png]] '''Decibel''' (symbol: dB) is a [[unit]] used to measure the intensity of a [[sound]] or the power level of an [[electrical signal]] by comparing it with a given level on a [[logarithmic scale]]. The decibel is a relative unit of measurement corresponding to one-tenth of a [[bel]] (B).<br />
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==Definition==<br />
The decibel is defined as ten times the [[logarithm]] to base 10 of the ratio of two power quantities. Mathematically, it is expressed as:<br />
: dB = 10 * log10(P1/P2)<br />
where P1 and P2 are the power levels.<br />
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For voltage or current ratios, the formula is:<br />
: dB = 20 * log10(V1/V2)<br />
where V1 and V2 are the voltages or currents.<br />
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==Applications==<br />
Decibels are commonly used in various fields such as [[acoustics]], [[electronics]], and [[control theory]]. They are used to express the ratio of one value of a physical property to another on a logarithmic scale.<br />
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===Acoustics===<br />
In acoustics, the decibel is used to measure [[sound pressure level]] (SPL). The reference level is typically the threshold of hearing, which is defined as 0 dB SPL.<br />
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===Electronics===<br />
In electronics, decibels are used to express the gain of an [[amplifier]], the loss of a [[transmission line]], or the [[signal-to-noise ratio]] (SNR) in a system.<br />
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==Common Reference Levels==<br />
Some common reference levels used in decibel measurements include:<br />
* [[dBm]]: Decibels relative to one milliwatt.<br />
* [[dBV]]: Decibels relative to one volt.<br />
* [[dBu]]: Decibels relative to 0.775 volts.<br />
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==Advantages==<br />
The use of decibels allows for a more manageable range of numbers when dealing with very large or very small values. It also simplifies the multiplication and division of ratios by converting them into addition and subtraction.<br />
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==History==<br />
The term "decibel" is derived from the [[bel]], named in honor of [[Alexander Graham Bell]]. The bel was too large for practical use, so the decibel, one-tenth of a bel, became the standard unit.<br />
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==See Also==<br />
* [[Sound level meter]]<br />
* [[Noise pollution]]<br />
* [[Hearing protection]]<br />
* [[Signal processing]]<br />
* [[Telecommunications]]<br />
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==References==<br />
{{Reflist}}<br />
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==External Links==<br />
{{Commons category|Decibel}}<br />
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[[Category:Units of measurement]]<br />
[[Category:Acoustics]]<br />
[[Category:Electronics]]<br />
[[Category:Logarithmic scales]]<br />
[[Category:Sound measurements]]<br />
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{{Acoustics-stub}}</div>Prab