The decibel
The decibel, or dB, is a logarithmic unit for expressing ratios, much beloved of engineers. Its popularity is due to the fact that it enables a wide range of numbers to be expressed conveniently.
Where we are talking about a ratio of two voltages then:
(A3.1)
which means that ‘A is twice B’ is often expressed as ‘A is 6dB greater than B', and ‘A is ten times B’ becomes ‘A is 20dB up on B'. Gain or attenuation of circuit blocks are very well expressed like this (a negative gain is an attenuation, or a ratio of less than one). The ratio is ‘output/input’.
dB’s are also used to express signal levels a lot. Here some reference ...
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