What is db, a scale used to measure in television networking?

dany: What is db, a scale used to measure in television networking?
Describe what is db and how to calculate db, a scale used to measure in television networking.

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Answer by Yin
Decibel
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For other uses, see Decibel (disambiguation).

The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power) relative to a specified or implied reference level. Its logarithmic nature allows very large or very small ratios to be represented by a convenient number, in a similar manner to scientific notation. Being essentially a ratio, it is a dimensionless unit. Decibels are useful for a wide variety of measurements in acoustics, physics, electronics and other disciplines.

The decibel is not an SI unit, although the International Committee for Weights and Measures (CIPM) has recommended its inclusion in the SI system. 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 (see below). The full name decibel follows the usual English capitalization rules for a common noun. The decibel symbol is often qualified with a suffix, which indicates which reference quantity has been assumed. For example, “dBm” indicates that the reference quantity is one milliwatt.

A decibel is one tenth of a bel (B). Devised by engineers of the Bell Telephone Laboratory to quantify the reduction in audio level over a 1 mile (1.6 km) length of standard telephone cable, the bel was originally called the transmission unit or TU, but was renamed in 1923 or 1924 in honor of the laboratory’s founder and telecommunications pioneer Alexander Graham Bell. In many situations, however, the bel proved inconveniently large, so the decibel has become more common.

Answer by rosie recipe
decibels – a measure of the loudness of sound

Answer by John F
A db is a decibel which is a logarithmic ratio of two quantities. As used in radio and television engineering, the decibel is defined as 10 log (power_1 / power_2) or as 20 log (voltage_1 / voltage_2).

For instance, if power_1 = 100 watts and power_2 = 10 watts, the ratio in db between them is 10 log(100/10) = 10 db.

Some handy conversions for db are:

10 db = 10 times
20 db = 100 times
30 db = 1000 times
3 db = 2 times
6 db = 4 times
36 db = 4000 times (see how adding db [30 + 6] is the same as algebraic multiplication [1000 x 4])