How to disable auto-adjusting of mic input level in Chrome in Mac OS?
If you are using  Audio application (like Skype) or like yours "language learning website that has an interactive feature that allows me to record myself"

you gave them permission to use your audio, otherwise they would not work.

Most of them have audio adjustment within them self (like Skype), so first look for it in your app you are using.

Microphone is used to send something back to the app. In turn it measures the Audio level and sends increase or decrees to your Mac. 

Mac is open to those requests (you gave it the permission).

The only way to stop this is revoke the permission, or check what audio setting the app it self has.

Stopping the Auto gain on your Mac would require application specific monitoring and blocking the audio gain adjustments, which could result in the app not working properly since it might not hear you well.

You also have a tool on your Mac that allows for more control and adjustments.


  Applications > Utilities > Audio Midi Setup