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Decibel - Typical abbreviations

Decibel - Typical abbreviations: Encyclopedia II - Decibel - Typical abbreviations

Decibel - Absolute measurements. dBm or dBmW dB(1 mW) — power measurement relative to 1 milliwatt. dBW dB(1 W) — same as dBm, with reference level of 1 watt. dBu or dBv dB(0.775 V) — (usually RMS) voltage amplitude referenced to 0.775 volt. Although dBu can be used with any impedance, dBu = dBm when the load is 600Ω. dBu is preferable, since dBv is easily confused with dBV. The "u" comes from "unlo ...

Decibel: Encyclopedia II - Decibel - Typical abbreviations

Decibel - Typical abbreviations

Decibel - Absolute measurements

dBm or dBmW dB(1 mW) — power measurement relative to 1 milliwatt. dBW dB(1 W) — same as dBm, with reference level of 1 watt.

dBu or dBv dB(0.775 V) — (usually RMS) voltage amplitude referenced to 0.775 volt. Although dBu can be used with any impedance, dBu = dBm when the load is 600Ω. dBu is preferable, since dBv is easily confused with dBV. The "u" comes from "unloaded". dBV dB(1 V) — (usually RMS) voltage amplitude of a signal in a wire, relative to 1 volt, not related to any impedance.

dB(SPL) dB(Sound Pressure Level) — 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 a dB is an absolute unit by itself.

dBm dB(mW) — power relative to 1 milliwatt. dBμ or dBu dB(μV/m) — electric field strength relative to 1 microvolt per metre. dBf dB(fW) — power relative to 1 femtowatt. dBW dB(W) — power relative to 1 watt. dBk dB(kW) — power relative to 1 kilowatt.

The term "measurement relative to" means so many dB greater, or smaller, than the quantity specified.

Examples:

3 dBm means 3 dB greater than 1 mW.
−6 dBm means 6 dB less than 1 mW.
0 dBm means no change from 1 mW, in other words 0 dBm is 1 mW.

Decibel - Relative measurements

dB(A), dB(B), and dB(C) weighting These symbols are often used to denote the use of different frequency weightings, 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 dB_A or dBA. According to ANSI standards, the preferred usage is to write L_A = x dB, as dBA implies a reference to an "A" unit, not an A-weighting. They are still used commonly as a shorthand for A-weighted measurements, however. dBd dB(dipole) — the forward gain of an antenna compared to a half-wave dipole antenna. dBi dB(isotropic) — the forward gain of an antenna compared to an idealized isotropic antenna. 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. In digital systems, 0 dBFS would equal the highest level (number) the processor is capable of representing. (Measured values are negative, since they are less than the maximum.) 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. dBC dB relative to carrier — in fiberoptic telecommunications, this indicates the relative levels of noise or sideband peak power, compared to the optical carrier power.