Allpass Filter Matlab Functions

Jon Harris wrote:

   ...


> It seems that you are implying that you can't make amplitude changes with an AP
> filter.  The standard technique that allows this is to combine the original
> unfiltered input with the AP filtered output in various proportions to achieve
> amplitude changes.  For example, it is easy to make a peaking or notch filter
> with a 2nd order AP.  At the center frequency, the AP output is shifted 180
> degrees from the input.  So adding that to the original gives you a notch and
> subtracting it gives you a peak.  Those are the easy cases.  I was wondering
> about other things such as shelving.

An all-pass in parallel with the original signal or another all-pass
isn't an all-pass structure. If you could affect amplitude with a
cascade of all-passes, they wouldn't be all-passes, would they? :-)

But now I see what you mean. If pressed to win a bet, I think I could do
it over a decade band, but it wouldn't be worth it. I'm thinking of
parallel channels two paths per channel roughly in quadrature and ...
Forget it!

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