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Why some IIR filter methods can't be used for High Pass Filters?

Started by commengr October 16, 2009
Hello,

I have a question that why can't some IIR filter design methods like
Impulse Invariant & Approximation of derivatives be used (or have poor
response) as band-pass, notch and high-pass filters


I think the reason for approximation of derivatives is that we can't go
beyond fs/4 on the Z-plane, so high-pass is out. But what is the issue with
band-stop and band-pass for a small pass-band?


Can some one explain? Robert, Glen?

commengr wrote:

> Hello, > > I have a question that why can't some IIR filter design methods like > Impulse Invariant & Approximation of derivatives be used (or have poor > response) as band-pass, notch and high-pass filters
Methods do work. It is just you who doesn't know how to use them properly. VLV
On Oct 16, 9:19=A0am, "commengr" <communications_engin...@yahoo.com>
wrote:
> Hello, > > I have a question that why can't some IIR filter design methods like > Impulse Invariant & Approximation of derivatives be used (or have poor > response) as band-pass, notch and high-pass filters > > I think the reason for approximation of derivatives is that we can't go > beyond fs/4 on the Z-plane, so high-pass is out. But what is the issue wi=
th
> band-stop and band-pass for a small pass-band? > > Can some one explain? Robert, Glen?
Aliasing is your problem if you blindly try to sample the impulse response of a highpas filter. Same issue with derivatives.
On Oct 16, 2:01=A0pm, Clay <c...@claysturner.com> wrote:
> On Oct 16, 9:19=A0am, "commengr" <communications_engin...@yahoo.com> > wrote: > > > Hello, > > > I have a question that why can't some IIR filter design methods like > > Impulse Invariant & Approximation of derivatives be used (or have poor > > response) as band-pass, notch and high-pass filters > > > I think the reason for approximation of derivatives is that we can't go > > beyond fs/4 on the Z-plane, so high-pass is out. But what is the issue =
with
> > band-stop and band-pass for a small pass-band? > > > Can some one explain? Robert, Glen? > > Aliasing is your problem if you blindly try to sample the impulse > response of a highpas filter. Same issue with derivatives.
what's being aliased is not the spectrum of your signal. an IIR filter designed by either method is still a legit LTI discrete-time system. but the frequency response that corresponds to the continuous- time impulse response that you've sampled will be an aliased version of the continuous-time frequency response. r b-j
> > >commengr wrote: > >> Hello, >> >> I have a question that why can't some IIR filter design methods like >> Impulse Invariant & Approximation of derivatives be used (or have poor >> response) as band-pass, notch and high-pass filters > >Methods do work. It is just you who doesn't know how to use them
properly.
> >VLV >
Look Vladimir, design a high pass digital IIR filter using the Approximation of derivatives method and we can have experts here as critics
>On Oct 16, 2:01=A0pm, Clay <c...@claysturner.com> wrote: >> On Oct 16, 9:19=A0am, "commengr" <communications_engin...@yahoo.com> >> wrote: >> >> > Hello, >> >> > I have a question that why can't some IIR filter design methods like >> > Impulse Invariant & Approximation of derivatives be used (or have
poor
>> > response) as band-pass, notch and high-pass filters >> >> > I think the reason for approximation of derivatives is that we can't
go
>> > beyond fs/4 on the Z-plane, so high-pass is out. But what is the
issue =
>with >> > band-stop and band-pass for a small pass-band? >> >> > Can some one explain? Robert, Glen? >> >> Aliasing is your problem if you blindly try to sample the impulse >> response of a highpas filter. Same issue with derivatives. > >what's being aliased is not the spectrum of your signal. an IIR >filter designed by either method is still a legit LTI discrete-time >system. but the frequency response that corresponds to the continuous- >time impulse response that you've sampled will be an aliased version >of the continuous-time frequency response. >
Effectively meaning that we lose the attenuation of the filter where we have aliasing in frequency domain?
>r b-j >
Syed
> > Methods do work. It is just you who doesn't know how to use >them > properly.
Omg, you are so arrogant....
>> >> Methods do work. It is just you who doesn't know how to use >them >> properly. > > >Omg, you are so arrogant.... > >
I think Vladimir is a wanna be Simon Cowell... of compdsp
commengr wrote:
>>> Methods do work. It is just you who doesn't know how to use >them >>> properly. >> >> Omg, you are so arrogant.... >> >> > > I think Vladimir is a wanna be Simon Cowell... of compdsp
Nevertheless, Vladimir is correct. The method works when it's properly applied. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
On Sun, 18 Oct 2009 09:35:33 +0200, Jake wrote:


>> Methods do work. It is just you who doesn't know how to use >them >> properly. > > > Omg, you are so arrogant....
He is. He's also very often right, so if you can excuse his arrogance long enough to glean value from what he says it's worth your while. -- www.wescottdesign.com