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From: Jason jia on 21 Jan 2010 17:28
I have a question regarding the design of IIR bandpass filter. From the desired filter shape, Ws1 = 0.4, Wp1 = 0.45, Wp2 = 0.55 ,Ws2 = 0.6, Rp = 0.5, Rs = 50. I'd like to know the coefficients of the numerator and denominator of transfer function in descending powers of z.
It seems like that order N=4, but why the coefficients have the length of 9 (b(0)......b(8). could anyone help me what the problem might be and how to resolve that?

[N,Wn]=ellipord([0.45 0.55],[0.4 0.6],0.1,30);
[b,a]=ellip(N,0.1,30,Wn)
fvtool(b,a);

Thanks a lot!

Jason
From: Rune Allnor on 22 Jan 2010 00:28
On 21 Jan, 23:26, "Jason jia" <fengrji...(a)gmail.com> wrote:
> I have a question regarding the design of IIR bandpass filter. From the desired filter shape, Ws1 = 0.4, Wp1 = 0.45, Wp2 = 0.55 ,Ws2 = 0.6, Rp = 0.5, Rs = 50. I'd like to know the coefficients of the numerator and denominator of transfer function in descending powers of z.
> It seems like that order N=4, but why the coefficients have the length of 9 (b(0)......b(8). could anyone help me what the problem might be and how to resolve that?

Think of one 4th order bandpass filter as a cascade of one
4th-order highpass and one 4th-order low-pass filter, and
things might start to make some sense.

Rune
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