How do you regulate noise complaints in your multi-family units?

[Eric Meinnert]

Hi all, 

I have a 3-plex, and the person living upstairs occasionally has people over or is just making noise at later times of the night. These times can range from normal times like 9-10pm to later times like 1-3am. The issue is that there is a different person sleeping in the unit below them. I don't live there, but I know that the person upstairs has a younger child that can be loud and they work until early morning time to time. How do you regulate this? I want to be respectul to both parties, but feel regulation of some sort might be necessary. Any input is appreciated.