Hearing without advanced sort of headphones - this sort of filtering improves clarity (9)
I believe the answer is:
trilinear
'this sort of filtering improves clarity' is the definition.
(as in trilinear filtering in computer graphics)
'hearing without advanced sort of headphones' is the wordplay.
'hearing' becomes 'trial' (I've seen this before).
'without' suggests deleting specific letters.
'advanced' becomes 'a'.
'sort of headphones' becomes 'inear' (in-ear headphones).
'trial' with 'a' taken out is 'tril'.
'tril'+'inear'='TRILINEAR'
(Another definition for trilinear that I've seen is " being like some plane shapes".)