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[Matlab] Butterworth lowpass filter design

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anix

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Hello guys,

I have this question:

A particular DSP system is sampled at 200 kHz, requires a digital Butterworth lowpass filter with a passband ripple of 1 dB at 40 kHz and a minimum stopband attenuation of 22 dB at 60 kHz.
Design the above filter using the impulse invariance method and the bilinear transformation method. Determine the order and the 3 dB cutoff frequency of the analog filter prototype using the formula given in the lecture notes, and then design the analog prototype filter using the M-file buttap of MATLAB. Transform the analog filter transfer function to the desired digital transfer function using the M-files impinvar and bilinear. Plot the magnitude and phase responses of both designs using the M-file fvtool. Compare the performances of the two filters. Show all calculation steps and the MATLAB codes used in the design.

I have this code but i am not sure if this generates what the question requires..can someone help me if this code is wrong?
Code:
Fd = 200000;         
fp = 40000;          
fs = 60000;          
Rp = 1;              
Rs = 22;             
Wp = 2 * pi * fp;    
Ws = 2 * pi * fs;    
[n, Wn] = buttord (Wp, Ws, Rp, Rs, 's');

[z,p,k] = buttap(n)       
[b,a]=butter(n,Wn,'s');   [bz, az]=impinvar(b,a,Fd) 
sys=tf(bz,az)             
h=fvtool(bz,az)           
set(h,'Analysis','phase') 
 
 
[num,den] = ZP2TF(z,p,k)  [numd,dend] = bilinear(num,den,Fd).
q=fvtool(numd,dend) 
set(q,'Analysis','phase')
 

hi guys
i have this question....who could help me?
design an HPF filter satisfying the following specifications:
|H(ω)| ≤ 0.021 , |ω| ≤ ωs = 0.35π
0.9790 ≤ |H(ω)| ≤ 1.021 , |ω| ≥ ωp = 0.5π
Plot the impulse response. Plot the magnitude, the phase and the group delay.
Verify your design. Try the filter on an audio signal.
 

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