Amplifier

An amplifier is an electronic device which increases the power (measured in watts) of an electrical signal. This involves using an external power source (generally mains electricity) to increase the amplitude while matching the input signal's wave shape.

For example, the signal created by a microphone is very low powered when it arrives at the next piece of equipment. This level would not be significant enough to get a good, consistent recording or even to reproduce clearly and effectively over a speaker system, therefore the first piece of gear a microphone signal hits is normally a pre-amp. The pre-amp simply raises the microphone signal level to a line-level signal which is useful for other processing and recording.

The ratio by which an amplifier affects the power of a signal is known as gain, which is normally measured in decibels in audio for practicality. Naturally, a gain greater than 1 (zero dB) represents an amplification.