Difference between revisions of "Bel"

From Hydrogenaudio Knowledgebase
Jump to: navigation, search
m (DB moved to Bel)
Line 1: Line 1:
{{title|dB}}
+
The '''bel''' is a logarithmical unit used to express relative difference in intensity or power between two signals, usually acoustic. Because of the fact that the Bel unit is too large for everyday use most of the times it is used as the more convenient '''decibel''' (abbreviated to '''dB''').
  
The '''decibel''' (abbreviated to '''dB''') is a logarithmical unit used to express relative difference in intensity or power between two signals, usually acoustic.
+
Decibel is equal to ten times the common logarithm of the ratio of the two levels.
  
It is equal to ten times the common logarithm of the ratio of the two levels.
+
::<math>{di\! f\!\! f} = \cdot \log_{10}\left(\frac{P_2}{P_1}\right )</math>
 +
 
 +
In case of the decibel we have a ''10'' factor:
  
 
::<math>{di\! f\!\! f} = 10 \cdot \log_{10}\left(\frac{P_2}{P_1}\right )</math>
 
::<math>{di\! f\!\! f} = 10 \cdot \log_{10}\left(\frac{P_2}{P_1}\right )</math>
 
The ''10'' factor comes from the fact the Bel unit is too large for everyday use; decibel is just more convenient.
 
  
 
There is a second definition of the decibel. In acoustics, it is used to express the ratio in sound pressure, because power is roughly proportional to the square of effective sound pressure.
 
There is a second definition of the decibel. In acoustics, it is used to express the ratio in sound pressure, because power is roughly proportional to the square of effective sound pressure.
Line 13: Line 13:
 
Let 'p' be pressure, 'P' power.
 
Let 'p' be pressure, 'P' power.
  
::<math>{di\! f\!\! f} = 10 \cdot \log_{10}\left(\frac{P_2}{P_1}\right )</math>
+
::<math>{di\! f\!\! f} = \cdot \log_{10}\left(\frac{P_2}{P_1}\right )</math>
 
    
 
    
::<math>{di\! f\!\! f} = 10 \cdot \log_{10}\left(\frac{p_2^2}{p_1^2}\right )</math>
+
::<math>{di\! f\!\! f} = \cdot \log_{10}\left(\frac{p_2^2}{p_1^2}\right )</math>
 
    
 
    
::<math>{di\! f\!\! f} = 20 \cdot \log_{10}\left(\frac{p_2}{p_1}\right )</math> because <math>\log_{10}(a^2) = 2 \cdot \log_{10}(a)</math>
+
::<math>{di\! f\!\! f} = 2 \cdot \log_{10}\left(\frac{p_2}{p_1}\right )</math> because <math>\log_{10}(a^2) = 2 \cdot \log_{10}(a)</math>
  
 
In this scale, it means an increase of 20 dB is equal to a ten-fold ratio, or 6 dB a two-fold ratio (<math>20 \cdot \log_{10}(2)</math> ''is approximately equal to 6'').
 
In this scale, it means an increase of 20 dB is equal to a ten-fold ratio, or 6 dB a two-fold ratio (<math>20 \cdot \log_{10}(2)</math> ''is approximately equal to 6'').
  
 
[[Category:Technical]]
 
[[Category:Technical]]

Revision as of 18:33, 14 June 2007

The bel is a logarithmical unit used to express relative difference in intensity or power between two signals, usually acoustic. Because of the fact that the Bel unit is too large for everyday use most of the times it is used as the more convenient decibel (abbreviated to dB).

Decibel is equal to ten times the common logarithm of the ratio of the two levels.

{di\! f\!\! f} = \cdot \log_{10}\left(\frac{P_2}{P_1}\right )

In case of the decibel we have a 10 factor:

{di\! f\!\! f} = 10 \cdot \log_{10}\left(\frac{P_2}{P_1}\right )

There is a second definition of the decibel. In acoustics, it is used to express the ratio in sound pressure, because power is roughly proportional to the square of effective sound pressure.

Let 'p' be pressure, 'P' power.

{di\! f\!\! f} = \cdot \log_{10}\left(\frac{P_2}{P_1}\right )
{di\! f\!\! f} = \cdot \log_{10}\left(\frac{p_2^2}{p_1^2}\right )
{di\! f\!\! f} = 2 \cdot \log_{10}\left(\frac{p_2}{p_1}\right ) because \log_{10}(a^2) = 2 \cdot \log_{10}(a)

In this scale, it means an increase of 20 dB is equal to a ten-fold ratio, or 6 dB a two-fold ratio (20 \cdot \log_{10}(2) is approximately equal to 6).