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> exa060702_2 , for example 6.6.2 and 6.7.2;
> to test buttord.m and butter.m;
> to design a Butterworth Bandpass digital filter.
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clear;
fp=[300 400];fs=[200 500];
rp=3;rs=18;
Fs=2000;
wp=fp*2*pi/Fs;ws=fs*2*pi/Fs;
>
> 求出阶次；
[n,wn]=buttord(wp/pi,ws/pi,rp,rs);
> 再设计 Butterworth 带通滤波器；
[b,a]=butter(n,wp/pi)
[h,w]=freqz(b,a,256,Fs);
h=20*log10(abs(h));
plot(w,h);grid;
ylabel('Bandpass DF')
xlabel(' Hz')