# What is a Decibel (dB)?

### Decibel (dB)

It is a unit for indicating the ratio between two physical quantities, commonly amounts of acoustic or electric power, or estimating the loudness of sounds.

## How Decibel Works

The decibel (symbol: dB) is a relative unit for estimation in correspondence to one-tenth of a bel (B). It indicates the ratio of one value of a power or root-power quantity to another on a logarithm scale. A level is a logarithmic quantity in decibels. A power ratio of 101/10, an approximate of 1.26, or a root-power ratio of 101⁄20 (approximately 1.12) applies to two signals whose levels differ.

The unit expresses a change in value (e.g., +1 dB or −1 dB) or an absolute value. The numeric value of the latter case indicates the ratio of a value to a set reference value; when utilized in such a way, they use letter codes to suffix the unit symbol; this way, the reference value is indicated. For example, experts use a common suffix "V" for the reference value of 1 volt (e.g., "20 dBV"). Two primary types of scaling of the decibel are usually in use.

It is expressed as ten times the logarithm in base 10 when expressing a power ratio. A change in power by a point of 10 is related to a 10 dB change in level. A difference in amplitude by a factor of 10 relates to a 20 dB change in level when expressing root-power quantities. The same value alters the corresponding power and root-power levels in linear systems, where there is proportionality in power to the square of the amplitude.

## Example of Decibel

For instance, there are two loudspeakers, the first playing a sound with power P1, and the second playing a louder version of the exact sound with power P2, but everything else (how far away, frequency) kept the equality. Using the decibel unit, the distinction in sound level between both speakers is 10 log (P2/P1) dB; that is, the log is to base 10. If the second creates two times as much power as the first, the contrast in dB will be 10 log (P2/P1) = 10 log 2 = 3 dB (approximation).

With this show on the graph, plot 10 log (P2/P1) against P2/P1. Following the example, if the second had 10 times the first power, the contrast in dB would be 10 log (P2/P1) = 10 log 10 = 10 dB. However, note that the decibel describes a ratio—the power radiated by either speaker isn't said, only the power ratio.

## Significance of Decibel

The decibel (dB) is a unit of logarithm generally used to estimate sound level. It is also commonly used in electronics, signals, and communication. The dB is a logarithmic way of expressing a ratio. Power, sound pressure, voltage or intensity, or many other things may be the ratio. The decibel is useful in the following fields: telephony, perception, acoustics, electronics, optics, and video and digital imaging.

## History of Decibel

The description of the decibel started in the calculation of transmission loss and power. The experts did so in the telephone of the 20th century. They completed the description in the Bell System in the United States. In honor of Alexander Graham Bell, they named the bel; however, they seldom use the bel. Instead, the decibel is effective for a wide range of calculations in science and engineering, mainly in acoustics, electronics, and control theory. The gains of amplifiers, attenuation of signals, and signal-to-noise ratios in electronics, are usually expressed in decibels.