Category Separators

I thought that I had done this with an older version of WP, but I’ve been searching for code where I can separate the categories, perhaps with a comma, or a dash.
Where it shows “filed under:” and then Category 1 Category 2 is where I’m looking to have something that would distinguish that there are two categories there, much like “filed under: Category 1, Category 2
Is it possible to do this? I was playing around with the templates-function-category (whatever the exact name is, I forget) but it didn’t work.
Please and thank you.