VOLUME (GAIN) CONTROL

Although often overlooked as an audio processor, a
simple volume (or gain) control fits the definition. Volume
adjustments can be made at several points within the
sound system, from the microphone inputs on the mixer all
the way to the inputs of the power amplifiers. Volume
levels are typically manipulated in one of two ways:
continuously variable adjustments, such as those made by
rotary potentiometers or faders, or fixed attenuation such
as that provided by a pad.
If adjusting a volume control adds amplification to the
audio signal, it is said to be providing gain. The volume
control that adjusts the amount of amplification added at a
mixer’s microphone input is sometimes referred to as a
gain (or trim) control, since the volume potentiometer is
controlling the gain of the microphone input’s preamplifier.
The function of this gain control is to match the input
sensitivity of the device to the level from the source.
A second type of volume control acts as an
attenuator, basically a continuously variable resistor that
adjusts the amount of signal allowed to pass through it. No
additional gain is provided by the volume control. The
volume control on an electric guitar is an attenuator. These
devices are often referred to as passive volume controls,
since they do not require any power. Occasionally, a
volume control will combine attenuation with gain. Faders
on a mixing console typically provide attenuation below
the "0" indication, and gain above that point.
Pads allow input stages to accommodate a variety of
signal levels. Microphone inputs typically feature an input
attenuation pad of some kind to reduce the sensitivity of
the input beyond that of the preamplifier gain control,
typically by 20 dB. A 50 dB pad is required for microphone
inputs that are designed to accept either microphone or
line level. The output stage of various devices can also
employ pads, usually to prevent overloading of the input
stage of the next device in the signal path. Care should be
taken to use pads only when necessary. For example,
using a 20 dB pad on a microphone input that does not
need additional attenuation will require additional gain be
added by the preamplifier, which adds more noise to the
audio signal.
While volume controls are the simplest of all audio
processors, they often the most misused. Correct
calibration of the various volume controls in a sound
system is known as proper gain structure.