# The unfiltered [filter] tag

I noticed today that we've got at least two distinct classes of question using the tag:

1. Mechanical filtration questions, e.g.
2. Signal processing questions, e.g.

There's also one that seems to involve concepts of both.

There are also quite a few questions where the tag is absent but could potentially be added; of these, I see around 5 that might use the tag in a mechanical filtration context and 7-8 that might use it in a signal processing context.

It seems clear that we need to be filtering these questions into multiple tags. I'm not sure whether two tags be enough to provide effective categorization, or if we should further subdivide the signal-related questions into smaller domains; for example, acoustic versus EM.

How can we best categorize these questions?

Please think about how any proposed tags could be distinguished using tag wiki excerpts, and whether we need any tag synonyms to support a particular set of tags.

• I don't particularly like the term 'mechanical filter'. In my mind that term means something along the lines of a vehicle suspension which acts as a high-pass mechanical filter. – Chris Mueller Nov 6 '15 at 21:31
• That's approximately why I stuck with "filtration" in the question to refer to the first category. But the terms seem inherently imprecise without qualification (which might imply that more granular tagging is desirable; water-filtration, air-filtration, etc.) – Air Nov 6 '15 at 21:35
• I would vote for the more granular categories like you suggest. – Chris Mueller Nov 6 '15 at 21:40
• I only really have any knowledge in the audio recording and environmental domains (as far as filters are concerned). I don't know what would be reasonable to propose with respect to the more EM-oriented domains (or mathematical, though I don't think we probably need a tag for that). – Air Nov 6 '15 at 21:51
• Perhaps "filter" should be disallowed. If someone attempts to use it, then show "filtration" and "signal-processing" as possibilities. I don't know if the SE system is capable of doing that. – Olin Lathrop Nov 8 '15 at 13:53

Since no-one has come forward with a specific proposal, here's what I've done to resolve the ambiguity:

1. Remove the existing tag from all questions. Until and unless it becomes a consistent and pernicious problem, there's no reason to request blacklisting (see also: MSE).
2. Add the new tags , and on a case-by-case basis.
3. No synonyms added at this time.

Tag wikis are TBD - in particular, and probably need wiki excerpts to distinguish their usage. However, has some overlap with another existing tag, . That's not my area of expertise and it's outside of the scope of this Meta discussion so I'm going to leave it be.