Al Clark wrote:

...

> The basic question is why does the hilbert filter with length 4i+1, for
> example 9 or 13 have better performance than a fir filter of length 4i-1,
> for example 7 or 11, even though the number of non zero coefficients is
> the same for the 4i+1 & 4i-1 filters. In the 4i+1 case, the first and
> last coefficients are zero, which allows the filter size to be reduced to
> a 4i-1 length.

The 4n+1 filter has two more points. It's just that the end two being
zero allows you the efficiency of not including them in the computation.
Try it with a low-pass. The same thing happens but it's harder to see in
the plots. Unless the window includes a pedestal, windowed FIRs are
always better with a window that's wider than the raw coefficients by two.

...

Jerry
--
Engineering is the art of making what you want from things you can get.
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