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. 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 Since it expresses a ratio of two (same unit) quantities, it is a dimensionless unit. In Dimensional analysis, a dimensionless quantity (or more precisely a quantity with the dimensions of 1) is a Quantity without any Physical units A decibel is one tenth of a bel (B).

The decibel is useful for a wide variety of measurements in science and engineering (e. Engineering is the Discipline and Profession of applying technical and scientific Knowledge and g. , acoustics and electronics) and other disciplines. Acoustics is the interdisciplinary science that deals with the study of Sound, Ultrasound and Infrasound (all mechanical waves in gases liquids and solids Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical 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.

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). deci- (symbol d) is a prefix in the SI system of units denoting a factor of 10−1 (1/10 The full name decibel follows the usual English capitalization rules for a common noun. English is a West Germanic language originating in England and is the First language for most people in the United Kingdom, the United States

The decibel symbol is often qualified with a suffix, which indicates which reference quantity or frequency weighting function has been used. A-weighting is the most commonly used of a family of curves defined in the International standard IEC616722003 and various national standards relating to the measurement of sound 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 definitions of the decibel and bel use base-10 logarithms. For a similar unit using natural logarithms to base e, see neper. For Neper as a mythological god see Neper (mythology, for the lunar crater named Neper see Neper (crater, and for the Scottish mathematician phycisist and

## History

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. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States 6 km) length of standard telephone cable. Basic principle A traditional landline telephone system also known as "plain old telephone service" (POTS, commonly handles both signaling and audio information 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. The Bell System which was named for Alexander Graham Bell, the technologist popularly credited with the invention of the Telephone, was a Trademark and WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout In many situations, however, the bel proved inconveniently large, so the decibel has become more common.

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. The International Committee for Weights and Measures is the English name of the Comité international des poids et mesures ( CIPM, sometimes written in English [2]

## 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. In Mathematics, the logarithm of a number to a given base is the power or Exponent to which the base must be raised in order to produce 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:

$L_\mathrm{dB} = 10 \log_{10} \bigg(\frac{P_1}{P_0}\bigg) \,$

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. In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it 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.

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. An electronic circuit is a closed path formed by the interconnection of Electronic components through which an Electric current can flow Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal Alternating current (AC Taking voltage as an example, this leads to the equation:

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

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. In Mathematics, the logarithm of a number to a given base is the power or Exponent to which the base must be raised in order to produce Scientific notation, also sometimes known as standard form or as exponential notation, is a way of writing numbers that accommodates values too large or small to be This allows one to clearly visualize huge changes of some quantity. (See Bode Plot and half logarithm graph. 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 )
• 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. Generally an amplifier or simply amp, is any device that changes usually increases the amplitude of a signal. 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.

## Uses

### Acoustics

Main article: Sound pressure

The decibel is commonly used in acoustics to quantify sound levels relative to some 0 dB reference. Sound pressure is the local Pressure deviation from the ambient (average or equilibrium pressure caused by a Sound Wave. Acoustics is the interdisciplinary science that deals with the study of Sound, Ultrasound and Infrasound (all mechanical waves in gases liquids and solids Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies 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 local Pressure deviation from the ambient (average or equilibrium pressure caused by a Sound Wave.

A reason for using the decibel is that the ear is capable of detecting a very large range of sound pressures. Sound pressure is the local Pressure deviation from the ambient (average or equilibrium pressure caused by a Sound Wave. The ratio of the sound pressure that causes permanent damage from short exposure to the limit that (undamaged) ears can hear is above a million. The word million In standard English, the -lli- in million is pronounced with an l-sound followed by a Because the power in a sound wave is proportional to the square of the pressure, the ratio of the maximum power to the minimum power is above one (short scale) trillion. The long and short scales are two different numerical systems used throughout the world Short scale is the English translation of the French To deal with such a range, logarithmic units are useful: the log of a trillion is 12, so this ratio represents a difference of 120 dB. Since the human ear is not equally sensitive to all the frequencies of sound within the entire spectrum, noise levels at maximum human sensitivity — for example, the higher harmonics of middle A (between 2 and 4 kHz) — are factored more heavily into sound descriptions using a process called frequency weighting. In Acoustics and Telecommunication, the harmonic of a Wave is a component Frequency of the signal that is an Integer La or A is the sixth Note ( Submediant) in the C major scale "A" is generally used as a standard for tuning The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. A weighting filter is used to emphasise or suppress some aspects of a phenomenon compared to others for measurement or other purposes

Further information: Examples of sound pressure and sound pressure levels

### Electronics

In electronics, the decibel is often used to express power or amplitude ratios (gains), in preference to arithmetic ratios or percentages. Sound pressure is the local Pressure deviation from the ambient (average or equilibrium pressure caused by a Sound Wave. In Electronics, gain is a measure of the ability of a circuit (often an Amplifier) to increase the power or Amplitude of a Arithmetic or arithmetics (from the Greek word αριθμός = number is the oldest and most elementary branch of mathematics used by almost everyone In Mathematics, a percentage is a way of expressing a number as a Fraction of 100 ( per cent meaning "per hundred" 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. Generally an amplifier or simply amp, is any device that changes usually increases the amplitude of a signal. An attenuator is an Electronic device that reduces the Amplitude or power of a signal without appreciably distorting its 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. In Classical physics, free space is a concept of Electromagnetic theory, corresponding to a theoretically "perfect" Vacuum, and sometimes A waveguide is a structure which guides waves such as Electromagnetic waves Light, or Sound waves Coaxial cable is a cable consisting of an inner conductor surrounded by a tubular insulating layer typically made from a flexible material with a high Dielectric constant, all An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length ) using a link budget. 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". For other uses see DBM (disambiguation dbm was the first of a family of simple Database engines originally written by Ken Zero dBm is the power level corresponding to a power of one milliwatt, and 1 dBm is one decibel greater (about 1. 259 mW).

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. In Mathematics, the root mean square (abbreviated RMS or rms) also known as the quadratic mean, is a statistical measure of the 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.

The bel is used to represent noise power levels in hard drive specifications. A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device It shares the same symbol (B) as the byte. A byte (pronounced "bite" baɪt is the basic unit of measurement of information storage in Computer science.

### Optics

In an optical link, if a known amount of optical power, in dBm (referenced to 1 mW), is launched into a fiber, and the losses, in dB (decibels), of each electronic component (e. An optical link is a Communications link that consists of a single end-to-end optical circuit For other uses see DBM (disambiguation dbm was the first of a family of simple Database engines originally written by Ken An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads g. , connectors, splices, and lengths of fiber) are known, the overall link loss may be quickly calculated by addition and subtraction of decibel quantities.

In spectrometry and optics, the blocking unit used to measure optical density is equivalent to −1 B. Barrier troops, also translated as blocking troops or blocking detachments (заградотряды заградительные отряды отряды заграждения In Optics, density is a unitless measure of the Transmittance of an optical element for a given length at a given Wavelength λ: 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. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value

## 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.

### Absolute measurements

#### Electric power

dBm or dBmW

dB(1 mW) — power measurement relative to 1 milliwatt. For other uses see DBM (disambiguation dbm was the first of a family of simple Database engines originally written by Ken XdBm = XdBW + 30.

dBW

dB(1 W) — similar to dBm, except the reference level is 1 watt. The Decibel watt or dBW is a unit for the measurement of the strength of a signal expressed in Decibels relative to one Watt. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. 0 dBW = +30 dBm; −30 dBW = 0 dBm; XdBW = XdBm − 30.

#### 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

dB(1 VRMS) — voltage relative to 1 volt, regardless of impedance. The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to A voltage source is any device or system that produces an Electromotive force between its terminals OR derives a secondary voltage from a primary For other uses see DBM (disambiguation dbm was the first of a family of simple Database engines originally written by Ken In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | In Mathematics, the root mean square (abbreviated RMS or rms) also known as the quadratic mean, is a statistical measure of the The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. [4]

dBu or dBv

dB(0. 775 VRMS) — voltage relative to 0. In Mathematics, the root mean square (abbreviated RMS or rms) also known as the quadratic mean, is a statistical measure of the The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. 775 volts. [4] Originally dBv, it was changed to dBu to avoid confusion with dBV. [5] 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

dB(1 mVRMS) — voltage relative to 1 millivolt, regardless of impedance. In Mathematics, the root mean square (abbreviated RMS or rms) also known as the quadratic mean, is a statistical measure of the The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. 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

dB(1 μVRMS) — voltage relative to 1 microvolt. In Mathematics, the root mean square (abbreviated RMS or rms) also known as the quadratic mean, is a statistical measure of the The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. Widely used in television and aerial amplifier specifications. 60 dBμV = 0 dBmV.

#### 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. Sound pressure is the local Pressure deviation from the ambient (average or equilibrium pressure caused by a Sound Wave. 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. 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 [6]

dB SIL

dB Sound Intensity Level — relative to 10−12 W/m2, which is roughly the threshold of human hearing in air. 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 The absolute threshold of hearing (ATH is the minimum Sound level of a Pure tone that an average ear with normal hearing can hear in a noiseless environment

dB SWL

dB Sound Power Level — relative to 10−12 W. Sound power level or acoustic power level is a logarithmic measure of the Sound power in comparison to a specified reference level

dB(A), dB(B), and dB(C)

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). A weighting filter is used to emphasise or suppress some aspects of a phenomenon compared to others for measurement or other purposes Other variations that may be seen are dBA or dBA. A-weighting is the most commonly used of a family of curves defined in the International standard IEC616722003 and various national standards relating to the measurement of sound 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. dBc ( decibels relative to the carrier) is the power ratio of a signal to a carrier signal expresses in Decibels.

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. Minimum audibility curve is a standardised graph of the Threshold of hearing versus frequency for an average human and is used as the reference level when measuring hearing

dB Q is sometimes used to denote weighted noise level, commonly using the ITU-R 468 noise weighting

dBZ

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

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

dBc

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. dBc ( decibels relative to the carrier) is the power ratio of a signal to a carrier signal expresses in Decibels. Compare dB(C), used in acoustics.

dBJ

dB(J) — energy relative to 1 joule. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity 1 joule = 1 watt per hertz, so power spectral density can be expressed in dBJ. In Statistical signal processing and Physics, the spectral density, power spectral density ( PSD) or energy spectral density (

dBm

dB(mW) — power relative to 1 milliwatt. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second.

dBμ or dBu

dB(μV/m) — electric field strength relative to 1 microvolt per meter. In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Compare the ambiguous use of dBu as a unit of voltage level.

dBf

dB(fW) — power relative to 1 femtowatt. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second.

dBW

dB(W) — power relative to 1 watt. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second.

dBk

dB(kW) — power relative to 1 kilowatt. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second.

### Relative measurements

dBd

dB(dipole) — the forward gain of an antenna compared to a half-wave dipole antenna. An antenna is a Transducer designed to transmit or Receive electromagnetic waves In other words antennas convert electromagnetic waves into A dipole antenna, developed by Heinrich Rudolph Hertz around 1886, is an antenna with a center- fed Driven element for transmitting

dBFS or dBfs

dB(full scale) — the amplitude of a signal (usually audio) compared to the maximum which a device can handle before clipping occurs. dBFS means " Decibels Full scale " It is an abbreviation for decibel amplitude levels in digital systems which have a maximum available level (like PCM In electronics and signal processing full scale or full code represents the maximum amplitude a system can present Amplitude is the magnitude of change in the oscillating variable with each Oscillation, within an oscillating system Clipping is a form of Distortion that limits a signal once it exceeds a threshold 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

dB(hertz) — bandwidth relative to 1 Hz. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. E. g. , 20 dB-Hz corresponds to a bandwidth of 100 Hz. Commonly used in link budget calculations. 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

dBi

dB(isotropic) — the forward gain of an antenna compared to the hypothetical isotropic antenna, which uniformly distributes energy in all directions. An isotropic radiator is a theoretical Point source of waves which exhibits the same magnitude or properties when measured in all directions

dBiC

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. Amplitude is the magnitude of change in the oscillating variable with each Oscillation, within an oscillating system Clipping is a form of Distortion that limits a signal once it exceeds a threshold Similar to dBFS, but also applicable to analog systems.

dBr

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.

dBrn

dB above reference noise. The symbol dBrn or dB(rn is an abbreviation for Decibels above Reference noise. In Telecommunication, reference noise is the magnitude of circuit Noise chosen as a reference for measurement See also dBrnC. dBrnC represents an audio level measurement typically in a telephone circuit relative to the level of circuit noise with the measurement of this level frequency-weighted by a standard

dBc

dB relative to carrier — in telecommunications, this indicates the relative levels of noise or sideband peak power, compared to the carrier power. dBc ( decibels relative to the carrier) is the power ratio of a signal to a carrier signal expresses in Decibels. Compare dBC, used in acoustics.

## 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. ^ a b Analog Devices : Virtual Design Center : Interactive Design Tools : Utilities : VRMS / dBm / dBu / dBV calculator
5. ^ What is the difference between dBv, dBu, dBV, dBm, dB SPL, and plain old dB? Why not just use regular voltage and power measurements? - rec. The cent is a logarithmic unit of measure used for musical intervals. dB drag racing is a competition rewarding the person who can produce the loudest sound inside a vehicle An equal-loudness contour is a measure of sound pressure ( dB SPL) over the Frequency spectrum for which a listener perceives a constant loudness 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 For Neper as a mythological god see Neper (mythology, for the lunar crater named Neper see Neper (crater, and for the Scottish mathematician phycisist and Noise pollution (or environmental noise) is displeasing human- or machine-created sound that disrupts the activity or balance of human or animal life The Richter magnitude scale, or more correctly local magnitude M L scale assigns a single number to quantify the amount of seismic energy released In Science, and especially in Physics and Telecommunication, noise is fluctuations in and the addition of external factors to the stream of target A weighting filter is used to emphasise or suppress some aspects of a phenomenon compared to others for measurement or other purposes audio. pro Audio Professional FAQ
6. ^ Morfey, C. FAQ is an Acronym for " Frequently Asked Question(s " 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 in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 37 - The Roman Senate annuls Tiberius ' will and proclaims Caligula emperor

## 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.