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Encyclopedia > Decibel

The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity) relative to a specified or implied reference level. Since it expresses a ratio of two (same unit) quantities, it is a dimensionless unit. A decibel is one tenth of a bel (B). The decibel (dB) is a measure of the ratio between two quantities. ... Logarithmic units are generic mathematical units in which we can express any quantities (physical or mathematical) that are defined as being proportional to values of a logarithm function. ... In physics, power (symbol: P) is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time. ... In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement...

The decibel is useful for a wide variety of measurements in science and engineering (e.g., acoustics and electronics) and other disciplines. It confers a number of advantages, such as the ability to conveniently represent very large or small numbers, a logarithmic scaling that roughly corresponds to the human perception of, for example, sound and light, and the ability to carry out multiplication of ratios by simple addition and subtraction. Engineering is the discipline and profession of applying scientific knowledge and utilizing natural laws and physical resources in order to design and implement materials, structures, machines, devices, systems, and processes that realize a desired objective and meet specified criteria. ... Acoustics is the interdisciplinary sciences that always deals with the study of sound, ultrasound and infrasound (all mechanical waves in gases, liquids, and solids). ... Surface mount electronic components Electronics is the study of the flow of charge through various materials and devices such as semiconductors, resistors, inductors, capacitors, nano-structures and vacuum tubes. ...

The decibel is not an SI unit. However, following the SI convention, the d is lowercase, as it represents the SI prefix deci-, and the B is capitalized, as it is an abbreviation of a name-derived unit (the bel). The full name decibel follows the usual English capitalization rules for a common noun. Look up si, Si, SI in Wiktionary, the free dictionary. ... deci- (symbol d) is a prefix in the SI system of units denoting a factor of 10âˆ’1 (1/10). ... The English language is a West Germanic language that originates in England. ... A noun, or noun substantive, is a word or phrase that refers to a person, place, thing, event, substance or quality. ...

The decibel symbol is often qualified with a suffix, which indicates which reference quantity or frequency weighting function has been used. For example, "dBm" indicates that the reference quantity is one milliwatt, while "dBu" is referenced to 0.775 volts. The practice of attaching a suffix in this way, though not permitted by SI,[1] is widely followed. The A-weighting curve is one of a family of curves defined in IEC179 and various other standards for use in sound level meters. ...

The definitions of the decibel and bel use base-10 logarithms. For a similar unit using natural logarithms to base e, see neper. A neper (Symbol: Np) is a unit of ratio. ...

The bel was originally devised by engineers of the Bell Telephone Laboratories to quantify the reduction in audio level over a 1 mile (approximately 1.6 km) length of standard telephone cable. It was originally called the transmission unit or TU, but was renamed in 1923 or 1924 in honor of the Bell System's founder and telecommunications pioneer Alexander Graham Bell. In many situations, however, the bel proved inconveniently large, so the decibel has become more common. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) was the main research and development arm of the United States Bell System. ... â€œMilesâ€ redirects here. ... For other uses, see Telephone (disambiguation). ... The Bell System was a trademark and service mark used by the United States telecommunications company American Telephone & Telegraph Company (AT&T) and its affiliated companies to co-brand their extensive circuit-switched telephone network and their affiliations with each other. ... Alexander Graham Bell (3 March 1847 â€“ 2 August 1922) was an eminent scientist, inventor and innovator who is credited with the invention of the telephone. ...

In April 2003, the International Committee for Weights and Measures (CIPM) considered a recommendation for the decibel's inclusion in the SI system and decided not to adopt that recommendation.[2] The International Committee for Weights and Measures is the English name of the ComitÃ© international des poids et mesures (CIPM, sometimes written in English ComitÃ© International des Poids et Mesures). ...

## Definitions

### Power

When referring to measurements of power or intensity, a ratio can be expressed in decibels by evaluating ten times the base-10 logarithm of the ratio of the measured quantity to the reference level. Thus, if L represents the ratio of a power value P1 to another power value P0, then LdB represents that ratio expressed in decibels and is calculated using the formula: Look up logarithm in Wiktionary, the free dictionary. ...

$L_mathrm{dB} = 10 log_{10} bigg(frac{P_1}{P_0}bigg) ,$

Naturally, P1 and P0 must have the same dimension (that is, must measure the same type of quantity), and must as necessary be converted to the same units before calculating the ratio of their numerical values. Note that if P1 = P0 in the above equation, then LdB = 0. If P1 is greater than P0 then LdB is positive; if P1 is less than P0 then LdB is negative. 2-dimensional renderings (ie. ...

Rearranging the above equation gives the following formula for P1 in terms of P0 and LdB:

$P_1 = 10^frac{L_mathrm{dB}}{10} P_0 ,$.

Since a bel is equal to ten decibels, the corresponding formulae for measurement in bels (LB) are

$L_mathrm{B} = log_{10} bigg(frac{P_1}{P_0}bigg) ,$
$P_1 = 10^{L_mathrm{B}} P_0 ,$.

### Amplitude, voltage and current

When referring to measurements of amplitude it is usual to consider the ratio of the squares of A1 (measured amplitude) and A0 (reference amplitude). This is because in most applications power is proportional to the square of amplitude. Thus the following definition is used:

$L_mathrm{dB} = 10 log_{10} bigg(frac{A_1^2}{A_0^2}bigg) = 20 log_{10} bigg(frac{A_1}{A_0}bigg) ,$

The formula may be rearranged to give

$A_1 = 10^frac{L_mathrm{dB}}{20} A_0 ,$

Similarly, in electrical circuits, dissipated power is typically proportional to the square of voltage or current when the impedance is held constant. Taking voltage as an example, this leads to the equation: An electronic circuit is an electrical circuit that also contains active electronic devices such as transistors or vacuum tubes. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... This box:      Electric current is the flow (movement) of electric charge. ... Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ...

$G_mathrm{dB} =20 log_{10} left (frac{V_1}{V_0} right ) quad mathrm quad$

where V1 is the voltage being measured, V0 is a specified reference voltage, and GdB is the power gain expressed in decibels. A similar formula holds for current.

### Examples

Note that all of these examples yield dimensionless answers in dB because they are relative ratios expressed in decibels.

• To calculate the ratio of 1 kW (one kilowatt, or 1000 watts) to 1 W in decibels, use the formula
$G_mathrm{dB} = 10 log_{10} bigg(frac{1000 mathrm{W}}{1 mathrm{W}}bigg) = 30 mathrm{dB} ,$
• To calculate the ratio of 1 mW (one milliwatt) to 10 W in decibels, use the formula
$G_mathrm{dB} = 10 log_{10} bigg(frac{.001 mathrm{W}}{10 mathrm{W}}bigg) = -40 mathrm{dB} ,$
• To find the power ratio corresponding to a 3 dB change in level, use the formula
$G = 10^frac{3}{10} times 1 = 1.99526... approx 2 ,$

It is seen that there is a 10 dB increase (decrease) for each factor 10 increase (decrease) in the ratio of the two power levels, and approximately a 3 dB increase (decrease) for every factor 2 increase (decrease). In exact terms, the factor is 103/10, or 1.9953, about 0.24% different from exactly 2. Similarly, an increase of 3 dB implies an increase in voltage by a factor of approximately √2, or about 1.41, an increase of 6 dB corresponds to approximately four times the power and twice the voltage, and so on. (In exact terms the power factor is 106/10, or about 3.9811, a relative error of about 0.5%.)

## Merits

The use of the decibel has a number of merits:

• The decibel's logarithmic nature means that a very large range of ratios can be represented by a convenient number, in a similar manner to scientific notation. This allows one to clearly visualize huge changes of some quantity. (See Bode Plot and half logarithm graph.)
• The mathematical properties of logarithms mean that the overall decibel gain of a multi-component system (such as consecutive amplifiers) can be calculated simply by summing the decibel gains of the individual components, rather than needing to multiply amplification factors. Essentially this is because log(A × B × C × ...) = log(A) + log(B) + log(C) + ...
• The human perception of, for example, sound or light, is, roughly speaking, such that a doubling of actual intensity causes perceived intensity to always increase by the same amount, irrespective of the original level. The decibel's logarithmic scale, in which a doubling of power or intensity always causes an increase of approximately 3 dB, corresponds to this perception.

Look up logarithm in Wiktionary, the free dictionary. ... Scientific notation, also known as standard form, is a notation for writing numbers that is often used by scientists and mathematicians to make it easier to write large and small numbers. ... The Bode plot for a first-order Butterworth filter A Bode plot, named after Hendrik Wade Bode, is usually a combination of a Bode magnitude plot and Bode phase plot: A Bode magnitude plot is a graph of log magnitude against log frequency often used in signal processing to show... An amplifier is a device which changes a small movement into a larger movement. ...

## Uses

### Acoustics

Main article: Sound pressure

The decibel is commonly used in acoustics to quantify sound levels relative to some 0 dB reference. The reference level is typically set at the threshold of perception of an average human and there are common comparisons used to illustrate different levels of sound pressure. Sound pressure is the pressure deviation from the local ambient pressure caused by a sound wave. ... Acoustics is the interdisciplinary sciences that always deals with the study of sound, ultrasound and infrasound (all mechanical waves in gases, liquids, and solids). ... This article is about audible acoustic waves. ... Sound pressure is the pressure deviation from the local ambient pressure caused by a sound wave. ...

Further information: Examples of sound pressure and sound pressure levels

It has been suggested that this article or section be merged into Sound pressure. ...

### Electronics

In electronics, the decibel is often used to express power or amplitude ratios (gains), in preference to arithmetic ratios or percentages. One advantage is that the total decibel gain of a series of components (such as amplifiers and attenuators) can be calculated simply by summing the decibel gains of the individual components. Similarly, in telecommunications, decibels are used to account for the gains and losses of a signal from a transmitter to a receiver through some medium (free space, wave guides, coax, fiber optics, etc.) using a link budget. In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system. ... Arithmetic tables for children, Lausanne, 1835 Arithmetic or arithmetics (from the Greek word Î±ÏÎ¹Î¸Î¼ÏŒÏ‚ = number) is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple day-to-day counting to advanced science and business calculations. ... A percentage is a way of expressing a proportion, a ratio or a fraction as a whole number, by using 100 as the denominator. ... For the British rock band of the same name, see Amplifier (band). ... An attenuator is a telecommunication device that reduces the amplitude of a signal without appreciably distorting its waveform. ... In physics, free space is a concept of electromagnetic theory, corresponding roughly to the vacuum, the baseline state of the electromagnetic field, or the replacement for the electromagnetic aether. ... In physics, optics, and telecommunication, a waveguide is a structure that confines and guides a propagating electromagnetic wave. ... Wikipedia does not yet have an article with this exact name. ... Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ... A link budget is the accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc. ...

The decibel unit can also be combined with a suffix to create an absolute unit of electric power. For example, it can be combined with "m" for "milliwatt" to produce the "dBm". Zero dBm is the power level corresponding to a power of one milliwatt, and 1 dBm is one decibel greater (about 1.259 mW). The correct title of this article is . ...

In professional audio, a popular unit is the dBu (see below for all the units). The "u" stands for "unloaded", and was probably chosen to be similar to lowercase "v", as dBv was the older name for the same thing. It was changed to avoid confusion with dBV. This unit (dBu) is an RMS measurement of voltage which uses as its reference 0.775 VRMS. Chosen for historical reasons, it is the voltage level which delivers 1 mW of power in a 600 ohm resistor, which used to be the standard reference impedance in almost all professional low-impedance audio circuits.[citation needed] In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ...

The bel is used to represent noise power levels in hard drive specifications. It shares the same symbol (B) as the byte. Typical hard drives of the mid-1990s. ... For the computer industry magazine, see Byte (magazine). ...

### Optics

In spectrometry and optics, the blocking unit used to measure optical density is equivalent to −1 B. In astronomy, the apparent magnitude measures the brightness of a star logarithmically, since, just as the ear responds logarithmically to acoustic power, the eye responds logarithmically to brightness; however astronomical magnitudes reverse the sign with respect to the bel, so that the brightest stars have the lowest magnitudes, and the magnitude increases for fainter stars. Optical density is the absorbance of an optical element for a given wavelength Î» per unit distance: Where: Although absorbance does not have true units, it is quite often reported in Absorbance Units or AU. Accordingly, optical density is measured in ODU, which are equivalent to AU cmâˆ’1. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ...

## Common reference levels and corresponding units

### "Absolute" and "relative" decibel measurements

Although decibel measurements are always relative to a reference level, if the numerical value of that reference is explicitly and exactly stated, then the decibel measurement is called an "absolute" measurement, in the sense that the exact value of the measured quantity can be recovered using the formula given earlier. For example, since dBm indicates power measurement relative to 1 milliwatt,

• 0 dBm means no change from 1 mW. Thus, 0 dBm is the power level corresponding to a power of exactly 1 mW.
• 3 dBm means 3 dB greater than 0 dBm. Thus, 3 dBm is the power level corresponding to 103/10 × 1 mW, or approximately 2 mW.
• −6 dBm means 6 dB less than 0 dBm. Thus, −6 dBm is the power level corresponding to 10−6/10 × 1 mW, or approximately 250 μW (0.25 mW).

If the numerical value of the reference is not explicitly stated, as in the dB gain of an amplifier, then the decibel measurement is purely relative. The practice of attaching a suffix to the basic dB unit, forming compound units such as dBm, dBu, dBA, etc, is not permitted by SI.[3] However, outside of documents adhering to SI units, the practice is very common as illustrated by the following examples. The International System of Units (symbol: SI) (for the French phrase Système International dUnités) is the most widely used system of units. ...

### Absolute measurements

#### Electric power

dB(1 mW) — power measurement relative to 1 milliwatt. XdBm = XdBW + 30.

dBW dBW is an abbreviation for the strength of a signal expressed in decibels relative to one Watt. ...

dB(1 W) — similar to dBm, except the reference level is 1 watt. 0 dBW = +30 dBm; −30 dBW = 0 dBm; XdBW = XdBm − 30.

For other uses, see Watt (disambiguation). ...

#### Voltage

Note that the decibel has a different definition when applied to voltage (as contrasted with power). See the "Definitions" section above.

A schematic showing the relationship between dBu (the voltage source) and dBm (the power dissipated as heat by the 600 Ω resistor)

dBV Image File history File links Relationship_between_dBu_and_dBm. ... Image File history File links Relationship_between_dBu_and_dBm. ... The decibel is a dimensionless unit (like percent) that is a measure of ratios on a logarithmic scale. ... It has been suggested that this article or section be merged with Current source. ... The correct title of this article is . ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ... Resistor symbols (American) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ...

dB(1 VRMS) — voltage relative to 1 volt, regardless of impedance.[4]

dBu or dBv In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... Josephson junction array chip developed by NIST as a standard volt. ...

dB(0.775 VRMS) — voltage relative to 0.775 volts.[5] Originally dBv, it was changed to dBu to avoid confusion with dBV.[citation needed] The "v" comes from "volt", while "u" comes from "unloaded". dBu can be used regardless of impedance, but is derived from a 600 Ω load dissipating 0 dBm (1 mW). Compare ambiguous use of dBu in radio engineering.

dBmV In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... Josephson junction array chip developed by NIST as a standard volt. ...

dB(1 mVRMS) — voltage relative to 1 millivolt, regardless of impedance. Widely used in cable television networks, where the nominal strength of a single TV signal at the receiver terminals is about 0 dBmV. Cable TV uses 75 Ω coaxial cable, so 0 dBmV corresponds to −48.75 dBm or ~13 nW.

dBμV or dBuV In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... Josephson junction array chip developed by NIST as a standard volt. ... Cable TV redirects here. ...

dB(1 μVRMS) — voltage relative to 1 microvolt. Widely used in television and aerial amplifier specifications. 60 dBμV = 0 dBmV.

In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... Josephson junction array chip developed by NIST as a standard volt. ...

#### Acoustics

dB(SPL)

dB (Sound Pressure Level) — for sound in air and other gases, relative to 20 micropascals (μPa) = 2×10−5 Pa, the quietest sound a human can hear. This is roughly the sound of a mosquito flying 3 metres away. This is often abbreviated to just "dB", which gives some the erroneous notion that "dB" is an absolute unit by itself. For sound in water and other liquids, a reference pressure of 1 μPa is used.[6]

dB SIL It has been suggested that this article or section be merged into Sound pressure. ... Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water and its boundaries. ...

dB Sound Intensity Level — relative to 10−12 W/m2, which is roughly the threshold of human hearing in air.

dB SWL Sound intensity level or acoustic intensity level is a logarithmic measure of the sound intensity in comparison to the reference level of 0 dB (decibels). ... Threshold of hearing is the sound pressure level SPL of 20 µPa (micropascals) = 2 × 10-5 pascal (Pa). ...

dB Sound Power Level — relative to 10−12 W.

dB(A), dB(B), and dB(C) Sound power level or acoustic power level is a logarithmic measure of the sound power in comparison to a specified reference level. ...

These symbols are often used to denote the use of different weighting filters, used to approximate the human ear's response to sound, although the measurement is still in dB (SPL). Other variations that may be seen are dBA or dBA. According to ANSI standards, the preferred usage is to write LA = x dB. Nevertheless, the units dBA and dB(A) are still commonly used as a shorthand for A-weighted measurements. Compare dBc, used in telecommunications.

dB HL or dB hearing level is used in Audiograms as a measure of hearing loss. The reference level varies with frequency according to a Minimum audibility curve as defined in ANSI and other standards, such that the resulting audiogram shows deviation from what is regarded as 'normal' hearing.[citation needed] It has been suggested that this article or section be merged with A-weighting. ... A response is the following: Often a response is the result of a stimulus. ... The A-weighting curve is one of a family of curves defined in IEC179 and various other standards for use in sound level meters. ... DBC may refer to: Detroit Boat Club, a historic rowing club. ...

dB Q is sometimes used to denote weighted noise level, commonly using the ITU-R 468 noise weighting[citation needed] The ITU-R 468-weighting curve (originally defined in CCIR recommendation 468) is widely used when measuring noise in audio systems, especially in the UK, Europe, and former countries of the British Empire such as Australia and South Africa. ...

dBZ

dB(Z) - energy of reflectivity (weather radar), or the amount of transmitted power returned to the radar receiver. Values above 15-20 dBZ usually indicate falling precipitation.[7]

#### Radio power, energy, and field strength

dBc DBC may refer to: Detroit Boat Club, a historic rowing club. ...

dBc — power relative to the power of the main carrier frequency; typically used to describe spurs, noise, channel crosstalk, and intermodal signals which may interfere with the carrier. Compare dB(C), used in acoustics.

dBJ Carrier frequency is the fundamental frequency used in both amplitude modulation and frequency modulation i. ...

dB(J) — energy relative to 1 joule. 1 joule = 1 watt per hertz, so power spectral density can be expressed in dBJ.

dBm The joule (IPA: or ) (symbol: J) is the SI unit of energy. ... In physics, the spectral density, or more correctly the power spectral density (PSD) of a given bandwidth of electromagnetic radiation is the total power in this bandwidth divided by the specified bandwidth. ...

dB(mW) — power relative to 1 milliwatt.

dBμ or dBu Milliwatt (SI symbol: mW) is a unit for measuring electrical power, equal to one-thousandth (10-3) of a watt. ...

dB(μV/m) — electric field strength relative to 1 microvolt per meter. Compare the ambiguous use of dBu as a unit of voltage level.

dBf In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. ... The volt is the SI derived unit for electric potential and voltage (derived from the ampere and watt). ... The metre, or meter (symbol: m) is the SI base unit of length. ...

dB(fW) — power relative to 1 femtowatt.

dBW The watt (symbol: W) is the SI derived unit for power. ...

dB(W) — power relative to 1 watt.

dBk For other uses, see Watt (disambiguation). ...

dB(kW) — power relative to 1 kilowatt.

The kilowatt (symbol: kW) is a unit for measuring power, equal to one thousand watts. ...

### Relative measurements

dBd

dB(dipole) — the forward gain of an antenna compared to a half-wave dipole antenna.

dBFS or dBfs A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ... A simple half-wave dipole antenna that a shortwave listener might build. ... dBFS means decibels full scale. It is an abbreviation for decibel amplitude levels in digital systems which have a maximum available level (like PCM encoding). ...

dB(full scale) — the amplitude of a signal (usually audio) compared to the maximum which a device can handle before clipping occurs. In digital systems, 0 dBFS (peak) would equal the highest level (number) the processor is capable of representing. Measured values are usually negative, since they should be less than the maximum.

dB-Hz The maximum amplitude a digital system can represent. ... For quantum-mechanical amplitude, see probability amplitude. ... An oscilloscope screen of an amplifier clipping. ...

dB(hertz) — bandwidth relative to 1 Hz. E.g., 20 dB-Hz corresponds to a bandwidth of 100 Hz. Commonly used in link budget calculations.

dB(isotropic) — the forward gain of an antenna compared to the hypothetical isotropic antenna, which uniformly distributes energy in all directions.

dBiC An isotropic antenna is an ideal antenna that radiates power with unit gain uniformly in all directions and is often used to reference antenna gains in wireless systems. ...

dB(isometric circular) — power measurement relative to a circularly polarized isometric antenna.

dBov or dBO

dB(overload) — the amplitude of a signal (usually audio) compared to the maximum which a device can handle before clipping occurs. Similar to dBFS, but also applicable to analog systems.

dBr Overload can refer to: Electrical overload, a situation where an electrical machine or system is subjected to a greater load than it was designed for. ... For quantum-mechanical amplitude, see probability amplitude. ... An oscilloscope screen of an amplifier clipping. ...

dB(relative) — simply a relative difference to something else, which is made apparent in context. The difference of a filter's response to nominal levels, for instance.

dBc In telecommunication, reference noise is the magnitude of circuit noise chosen as a reference for measurement. ...  dBrnC The correct title of this article is dBrnC. It appears here with an initial capital letter due to technical restrictions. ... DBC may refer to: Detroit Boat Club, a historic rowing club. ...

dB relative to carrier — in telecommunications, this indicates the relative levels of noise or sideband peak power, compared to the carrier power. Compare dBC, used in acoustics.

Copy of the original phone of Alexander Graham Bell at the MusÃ©e des Arts et MÃ©tiers in Paris Telecommunication is the assisted transmission of signals over a distance for the purpose of communication. ...

The cent is a logarithmic unit of measure used for musical intervals. ... Properly spelled dB drag racing, with dB meaning deciBels of sound pressure level (SPL). ... An equal-loudness contour is a measure of sound pressure (dB SPL), over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. ... The ITU-R 468-weighting curve (originally defined in CCIR recommendation 468) is widely used when measuring noise in audio systems, especially in the UK, Europe, and former countries of the British Empire such as Australia and South Africa. ... A neper (Symbol: Np) is a unit of ratio. ... Environmental Noise is unwanted sound, which may cause both nuisance and damage to health. ... The Richter magnitude scale, or more correctly local magnitude ML scale, assigns a single number to quantify the amount of seismic energy released by an earthquake. ... In science, and especially in physics and telecommunication, noise is fluctuations in and the addition of external factors to the stream of target information (signal) being received at a detector. ... It has been suggested that this article or section be merged with A-weighting. ...

## Footnotes

1. ^ Taylor 1995, Guide for the Use of the International System of Units (SI), NIST Special Publication SP811
2. ^ Consultative Committee for Units, Meeting minutes, Section 3
3. ^ Taylor 1995, SP811
4. ^ Analog Devices : Virtual Design Center : Interactive Design Tools : Utilities : VRMS / dBm / dBu / dBV calculator
5. ^ Analog Devices : Virtual Design Center : Interactive Design Tools : Utilities : VRMS / dBm / dBu / dBV calculator
6. ^ Morfey, C. L. (2001). Dictionary of Acoustics. Academic Press, San Diego.
7. ^ Radar FAQ from WSI. Retrieved on 2008-03-18.

2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 77th day of the year (78th in leap years) in the Gregorian calendar. ...

## References

• Martin, W.H. (1929). "DeciBel--The New Name for the Transmission Unit". Bell System Technical Journal January.
• STEVENS SS (1957). "On the psychophysical law". Psychol Rev 64 (3): 153–81. PMID 13441853.

Results from FactBites:

 Decibels (510 words) The decibel scale is a reflection of the logarithmic response of the human ear to changes in sound intensity: The sound intensity in decibels above the standard threshold of hearing is calculated as a logarithm. In fact, the use of the factor of 10 in the definition of the decibel is to create a unit which is about the least detectable change in sound intensity.
 decibel (1153 words) The decibel is made a unit by specifying the magnitude of one element of the ratio; this is the reference level. For power, the decibel is 10 times the common logarithm of the ratio of the power of the signal being described to the power of the reference level. In acoustics, decibels are used to express sound intensity levels (10 times the common logarithm of the ratio between the measured intensity and a reference intensity), and sound pressure levels (20 times the common logarithm of the ratio between the measured pressure level and a reference pressure level).
More results at FactBites »

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