Gain is the number of times that the output of a circuit is greater than the input. Gain and volume are terms often used interchangeably but this can lead to confusion, especially with equipment, such as mixing desks, which has both. True gain controls are also found on many effects units, and on some amplifiers.
All amplifiers have the property of gain. Amplifiers that drive loudspeakers consist of a number of linked amplification stages, each with its own gain factor. The total gain of the complete amplifier is the sum of the gain of these individual stages.
Volume controls act on either the input signal or the signal passing between two amplifier stages. They alter the level of the signal and can even reduce it to zero. They do not alter the actual gain of any of the stages. Gain controls, on the other hand, do alter the gain of an amplification stage. Their minimum setting is usually a gain of 1, which means that the level of the output signal is the same as the input. Their maximum setting may be designed to make the stage distort for special effect, although the normal use of these controls is to present an output level from the controlled stage which is at an optimum level succeeding stages to operate at maximum efficiency, no matter what the level of the input signal. In use, gain controls are turned up to give as high a signal level as possible to the following stage without causing distortion – unless distortion is required.
Gain before feedback is the maximum amount of gain that can be achieved in a sound system before feedback occurs.