Automatic gain control keeps a speaker's voice at a consistent target level regardless of how loudly they talk or how far they sit from the microphone. It continuously estimates the incoming level and applies gain to push quiet talkers up and loud ones down, so a meeting doesn't force everyone to ride their own volume. The challenge is doing this without pumping audible level swings, without amplifying background noise during pauses, and without fighting the other processors around it. In WebRTC the modern implementation is AGC2, an adaptive digital design that replaced the older analog-style loop for steadier results across the wildly varying microphones people actually use.
