1 MSC corresponded to the loss of power over one mile (approximately 1.6 km) of standard telephone cable at a frequency of 5000 radians per second (795.8 Hz), and matched closely the smallest attenuation detectable to a listener. Until the mid-1920s, the unit for loss was Miles of Standard Cable (MSC). The decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. 5.8 List of suffixes in alphabetical order.5.5 Radio power, energy, and field strength.3.3 Representation of addition operations.3.2 Representation of multiplication operations.

2.3 Relationship between power and root-power levels.In electronics, the gains of amplifiers, attenuation of signals, and signal-to-noise ratios are often expressed in decibels.Īn example scale showing power ratios x, amplitude ratios √ x, and dB equivalents 10 log 10 x. Instead, the decibel is used for a wide variety of measurements in science and engineering, most prominently in acoustics, electronics, and control theory. The bel was named in honor of Alexander Graham Bell, but the bel is seldom used. The definition of the decibel originated in the measurement of transmission loss and power in telephony of the early 20th century in the Bell System in the United States. The decibel scales differ by a factor of two, so that the related power and root-power levels change by the same value in linear systems, where power is proportional to the square of amplitude. When expressing root-power quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level. When expressing a power ratio, it is defined as ten times the logarithm in base 10. Two principal types of scaling of the decibel are in common use. For example, for the reference value of 1 volt, a common suffix is ' V' (e.g., '20 dBV'). In the latter case, the numeric value expresses the ratio of a value to a fixed reference value when used in this way, the unit symbol is often suffixed with letter codes that indicate the reference value. The unit expresses a relative change or an absolute value. Two signals whose levels differ by one decibel have a power ratio of 10 1/10 (approximately 1.26) or root-power ratio of 10 1⁄ 20 (approximately 1.12). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel ( B).

For other uses, see Decibel (disambiguation). For use of this unit in sound measurements, see Sound pressure level. This article is about the logarithmic unit.

Decibel app