The Filters pane always says “Select a Clip”. I have 4 clips (2 video, and 2 detached audio)… no matter which one I select (by clicking on it which puts a white box around it), filters remain unavailable.
I am attaching a screen shot.
(I believe this is the same as the seemingly unresolved issue raised at Sélection and filter's windows! )
When you select in the timeline and it adds a white outline instead of red that means you have selected a group of clips (that you made). You cannot edit filters for multiple selected clips. A group is a multi selection. You must select one:
If the group is already selected Ctrl-click the one to use.
If the group is not selected Alt-click to select a single member of a group.
I didn’t think I was working with a group… I was trying to apply a filter to a single track, which had a single piece of footage (no splits/edits) from start to end. Hmm.
At any rate, I went on to another project and tried again. I got it to work, but very inconsistently, so I think I’m still doing something wrong. Maybe the fact that I have detached audio tracks is making a difference? (I’m actually trying to apply filters to audio tracks.)
Right click any clip that is in a group and choose to ungroup if you do not want that group.
A clip is different than a track. If you want to add a filter to a track, you need to select the track by clicking its header in the column at the far left of the Timeline panel.
Sorry for the confusion in terminology. The single track had only a single clip (a single piece of footage, as I put it). My point was that, as far as I knew, by clicking anywhere on the track, I was already clicking on a single clip, and not one that was part of a group. But I just tried your instruction to right-click the one-and-only clip on the track, and select “ungroup”, and sure enough, the red outline appeared around the clip (which was still the entirety of the track). I still could not apply a filter (the box still said to select a clip, even though I could see the clip/track outlined in red), however if I then clicked on another track, and then went back to the one I started with, it was now available to have a filter applied. I suspect I just lack some understanding of the basics which is why things do not necessarily behave as I’d expect.
I thought maybe I just don’t understand what grouping is and how it happens. I just tried searching the Help and the manual for “group” to see if I was misunderstanding something there, but didn’t find anything.
The shortcut for creating a group is Ctrl-G (on Windows/Linux - maybe CMD-G on Mac?). Perhaps you have pressed Ctrl-G by accident - ?
Well, since apparently I had grouped items even though I never intended to group anything, apparently I did something by accident. 
I think I may just not understand what a group is. Is it a combination of multiple clips that reside on a single track? A combination of multiple clips that reside on different tracks? Or can it be either of those? Or is it something else?
