This might be a strange question - but most of the Type 3 LPF I'm seeing are having this in common for $h[n]$, assuming $h[n]$ is real:
- We cannot have outermost element of h[n] lower than middle elements
- (or) Have middle element lower than outermost elements.
Eg: if filter coefficients are $[3,2,1,0,-1,-2,-3]$, it there any restriction for a type $3$ filter to not have $[1,2,3,0,-3,-2,-1]$ as a possible LPF $h[n]$?
(Please excuse my ignorance if this is a basic question - I'm quite new FIR Filter design). And I've gone through quite a few design docs before asking this question - none of them mention this, so I'm guessing this is not a req? Yet the diagrams seem to indicate this, hence the question...