Automatic Gain Control or AGC is a circuit design which maintain the same level of amplification ... On the electroschematics.com site you can find some AGC schematics, just use the seach box.

This Design Idea works with other types of AGC amplifiers, too [1]. But in this case, an analog switch is unnecessary. In these circuits, a sample-and-hold amplifier should be connected between the ...

[Alan’s] c ircuit isn’t new, he states right in the video that various audio limiting, compressing, and automatic gain control circuits have been passed around the internet for years.