[scilab-Users] Cascaded IIR filter design

[Celso Co]

You may want to consider some means of manipulating poles and zeros in the
attached file.  Celso

-----Original Message-----
From: Adelson Santos de Oliveira [mailto:adelson.oliveira at gmail.com]
Sent: Saturday, July 25, 2009 10:03 AM
To: users at lists.scilab.org
Subject: Re: [scilab-Users] Cascaded IIR filter design


Sorry,
I would like to help but I can make only general comments. I would not
go into the subject of your work.
If hz were a Scilab polynomial, getting poles and zeroes would be
straightforward from numerator and denominator ...

I can only suggest you find a way to decompose hz into scilab objects
(polys, ....),

Good luck,

Adelson

Markus Svilans escreveu:
> Hi Adelson,
>
> Thanks for your response.
> I think hz must be a Scilab rational polynomial. Here are its contents:
>
> -->hz
> hz  =
>
>                                       2            3
> 4            5            6  - 0.0513754 + 0.0469923z - 0.0057700z +
> 2.282D-17z + 0.0057700z - 0.0469923z + 0.0513754z
> --------------------------------------------------------------------------
-------------
>
>                                           2            3
> 4            5   6             0.5046613 - 1.0416559z + 2.4270369z -
> 2.6222075z + 2.9969513z - 1.6458787z + z
>
> From what I have been able to research so far, I am starting to feel
> that it's not possible to get Scilab to directly return the a,b
> cascaded IIR coefficients.
>
> Perhaps, could you lend your expertise on these related questions:
> 1. How to get the poles of hz?
> 2. How to get the zeroes of hz?
>
> Knowing the poles and zeroes, I can hope to derive the IIR
> coefficients by hand.
>
> Thanks very much,
> Markus.
>
>
>
> Adelson Santos de Oliveira wrote:
>> Sorry,
>>
>> I did not analyse your program. I supposed that hz is a polinomial
>> according to SCILAB definition. See the following example and check
>> if you can adapt it to your needs,
>>
>>
>> Polz=poly([1,2,3],'Z','coefs')       <= this define a polynomial in
>> variable Z, maybe your hz is not a polynomial for SCILAB
>>
>> coefz=coeff(Polz)                        <= this will return the
>> coefficients 1, 2, and 3
>>
>>
>> Markus Svilans escreveu:
>>> Adelson,
>>>
>>> Thanks for your response.
>>>
>>> It doesn't seem to work. The error message I get is:
>>>
>>> --
>>> Function not defined for given argument type(s),
>>>
>>>  check arguments or define function %r_coeff for overloading.
>>> --
>>>
>>> I'm looking for a way to get the b0, b1, a1, b2, a2, ...
>>> coefficients required for a cascaded IIR. From what I understand,
>>> there is an algorithm by which they are computed from the z-domain
>>> coefficients hz.
>>>
>>> Regards,
>>> Markus.
>>>
>>>
>>> Adelson Santos de Oliveira wrote:
>>>> Do you mean,
>>>>
>>>> coef_hz=coeff(hz) ?
>>>>
>>>> coef_hz is a vector with the coefficients of hz.
>>>>
>>>> coefhz=coeff
>>>> Markus Svilans escreveu:
>>>>> Hello,
>>>>>
>>>>> I would like to use Scilab to design a cascaded IIR filter.
>>>>>
>>>>> I'm able to design a filter using iir(), as in the following example
>>>>> code:
>>>>>
>>>>> ystr=[ 'type (lp, hp, bp, sb) ';
>>>>>    'order (integer)';
>>>>>    'design (butt, cheb1, cheb2 , ellip)' ;
>>>>>    'cut-off frequencies (2-vector in [0, 0.5])';
>>>>>    'error values  0 delta(1),delta(2) 1 '];
>>>>> w = x_mdialog('Choose filter type and parameters',...
>>>>>    ystr,['bp';'3';'ellip';'0.15 0.25';'0.08 0.035'])
>>>>>
>>>>> if w<>[] then
>>>>>  hz=iir(evstr(w(2)),w(1),w(3),evstr(w(4)),evstr(w(5)));
>>>>>  [hzm,fr]=frmag(hz,256);
>>>>>  xselect();
>>>>>  plot2d(fr',hzm')
>>>>>  xtitle('Discrete IIR filter '+'( '+ w(3)+' ) ',' ',' ');
>>>>>
>>>>>  hz
>>>>> end
>>>>>
>>>>> My question is, how can I convert the z domain expression in hz to a
>>>>> set of coefficients suitable for use in a cascaded IIR filter
>>>>> implementation? Any help would be greatly appreciated.
>>>>>
>>>>> Best regards,
>>>>> Markus.
>>>>>
>>>>> (also posted in the comp.soft-sys.math.scilab group)
>>>>>
>>>>>
>>>>
>>>
>>>
>>
>
>
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