Back in 1998 I played around with an AGC based on a vogad chip, it got the job done via line out on a Yamaha EMX300 to a cassette recorder but the THD was around 1.5%. Around 2003, my mentor, a broadcast engineer in his retirement had worked out how to build an AGC/ALC based on either a TL072 or TL074 and a handful of caps, resistors and diodes on a strip veroboard. The use-cases included an intercom system in community radio broadcast studio, the signal levels used in Australian Broadcasting Corporation which used 1KHz reference at either 1 millivolt and 1 microvolt, the common issue of clueless audio console operators in churches. On this particular project he encountered a fractured track on this veroboard which was resolved then testing revealed that the AGC achived less than 0.002% THD. He wanted to construct and sell these AGC's to keep busy in retirement and that was about the time I moved interstate and lost contact with him. He has since then passed but one of his friends that was involved in that project occasionally shows up in these types of forums. I am curious to know if the schematic or any of that project has been made open source?
are you serious do you realize what those quoted specs mean to the audio industry in general....?