Automatic Gain Control (AGC) is present in a multitude of different electronics and even a few biological applications. Simply put, it is a feature that automatically increases the signal coming out of an output into an input. Whether this is a visual, audio, electronic, or virtually any other kind of signal, automatic gain control enables you to enjoy a consistent experience in an environment where signal strength varies.
Automatic gain control exists in biological forms as well. For example, when you walk into a dimly lit room, it can be very difficult to find your way around. Over time, your eyes adjust and you’re able to see the outlines of various objects in the room. This is also the reason why you experience a blinding amount of light when you walk out of a dark room as your eyes have yet to adjust their internal automatic gain control to the increase in perceivable light.
The principal is applied in a very similar way to electronics. An AM radio incorporates automatic gain control because the audio played through various stations would vary to an extreme. Without AGC, a strong signal would appear much louder than a weaker signal. ACG steps in and boost the signal received on the AM band where lower signal strength is detected and reduces the signal strength on a strong one. The gain in this case is a literal gain (or increase) of the available signal.
Automatic gain control is also used for telephone recordings. If you’ve ever picked up a second receiver on a shared phone line (we’re talking traditional phones here), you may have noticed that everyone on your side of the conversation sounds significantly louder than those in a remote location. In order to record a phone call without one party sounding extremely loud, AGC needs to knock down the local and boost the remote parties so they can be recorded at an even volume.
Automatic gain controls exist in many different electronics used every day, even now. Televisions, musical amplifiers, radar, radios, etc. all use automatic gain control to offer a consistent experience to the user without them even knowing that it’s going on.