Limiter

Technically a compressor with a very high ratio and a nearly instant attack, sitting last in the chain so nothing gets past the point you chose. On an upload its job is safety: a cough or a door slam that would otherwise clip gets caught and flattened.

Set the ceiling slightly below zero, around minus one dBTP, because encoding to AAC can push true peaks above whatever your meter showed you. And keep it there to catch peaks. Driving a signal hard into a limiter to make it louder squashes the life out of speech.