c++ How to reduce size/complexity of class? [on hold]

I have an audio plugin with a top level class that handles all the top level stuff. Lots of operations are handled by other classes that are somewhat self-contained, but at some point, this top level class keeps growing. I'd love to create a helper class or two that handle some specific operations, like file reading and writing, but then the helper class ends up needing to know about several functions and variables inside the top level class. It just seems messy.

Is there a design pattern that I'm missing that could help?