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Decibel is a measure of sound levels. It is difficult to do anything in audio and not encounter the decibel. The decibel offers a precise calculation that quantifies properties of an audio signal in a very useful form. The decibel offers a perceptually meaningful description of amplitude, one that the ears and brain can make sense of.

The decibel appears in some form on almost every faceplate and user interface of every signal processor in the recording studio. Understanding the meaning of quantities in decibels is essential to understanding sound effects.

Decibel Definition

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Decibel is a measure to quantify the sound level. It is given by the logarithmic ratio of power, intensity or sound pressure etc. Basically it is a logarithmic ratio of physical quantity.

Decibel Formula

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The power equation that absolutely defines the decibel (dB) :
dB = 10log$\frac{P_{1}}{P_{2}}$

So, the decibel is ten times the logarithm of the ratio of two powers.

Decibel Levels

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The different decibel levels are listed below :

Sound Source Decibel Level (dB)
Jet takeoff
120
Construction site
110
Shout
100
Heavy truck
90
Urban street 80
Automobile interior
70
Normal conversation
60
Office
50
Broadcast studio
20
Rustling leaves 10

Decibel Conversion

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In general decibel is considered as the logarithmic ratio of powers. This power ratio can be converted in terms of voltage and current.

We know that,
dB = 10log$\frac{P_{1}}{P_{2}}$

Power is proportional to square of the voltage and current.
P = $I^{2}$R
P = $\frac{V^{2}}{R}$

So, the equation for dB in terms of voltage and current is,
dB = 20log$\frac{V_{1}}{V_{2}}$

dB = 20log$\frac{I_{1}}{I_{2}}$
Decibel meter is used to detect the sound levels. It is very much used to recognize the noise, which helps to reduce the noise pollution. It is also known as sound level meter or sound meter.
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