Page "Amplifier" Paragraph 1

In an electronic amplifier, the input " signal " is usually a voltage or a current.

Other types exist ; a fluidic amplifier increases the power of signals represented as flow of gas or liquid, for example.

Amplifiers may be classified in a variety of ways depending on their application, the frequency range they cover, or the active devices used.

Ideally an amplifier increases the power of a signal without otherwise altering it ; practical amplifiers have finite distortion and noise which they invariably add to the signal.