The most common and most likely answer to this crossword clue is the 9 letter word TRILINEAR
I've seen this crossword clue in Independent
T
R
I
L
I
N
E
A
R
Buddy explains!
The straight part
We know that "this sort of filtering improves clarity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case this sort of filtering improves clarity = trilinear.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TRILINEAR mean?
TRILINEAR adjective- Having, or bounded by, three lines.