🚀 go-pugleaf

karsh@trifolium.esd.sgi.com (Bruce Karsh) writes:

>In article <9441@pasteur.Berkeley.EDU> maverick@fir.Berkeley.EDU (Vance Maverick) writes:

>>Is there a recipe for generating the "complement" of a given filter?  Or
>>for generating a pair of filters which are complementary in this sense? 
>>I've seen the basic transformations between lowpass and highpass
>>filters, and I don't think they qualify.

>Generate one of the too signals, e.g. the low passed signal.  Subtract it
>from the original signal to get the high passed signal.

>			Bruce Karsh
>			karsh@sgi.com

This is a nice idea, but it won't work in general.

If H(z) is the low pass prototype, then, 1 - H(z)
is a high pass ?  No, sorry this does not work.

i.e., say H(e^jw) = j  (at a certain low frequency).
Then 1 - H(e^jw) = 1 - j (which is nothing like a high pass).

i.e. simple subtraction doesn't consider the phase response of
H(z).


Something must have been written on this, what about Quadrature Mirror
Filterbanks ??
--
Wilf LeBlanc                                 Carleton University
Internet: wilf@sce.carleton.ca               Systems & Computer Eng.
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