Genres: Theirs or Mine?

No, you can multi-select several albums like the first 3 that I have selected here, then click the (…) button and then Edit in the menu:

Then to to the Album Editor and you can add/remove genres for all selected albums at once:

I described how to multi-select in detail here because the Roon help is not exhaustive:

(Note: There is a limit to how many albums you can select at once, I think 1000. In any case, it will be slow to apply the changes if you have that many selected, so be patient in this case)

1 Like