I am recording a song and the instrumental has a lot of very loud parts and a lot of very soft parts. I could use normalization or compression, but I don’t want to touch the instrumental or make the whole vocal track the same volume. Is there a way to make the volume of the vocal tracks go up and down based on the instrumental track?
Envelope follower. Steve’s Dynamic-Mirror plugin can do that.
Not possible with the built-in ones?
You could do it with the built-in Envelope tool: Envelope Tool - Audacity Manual
(but that will take much more time and effort than using my Dynamic-Mirror plugin).