% ex72.m fs=10000; fs2=fs/2; f1=1000; f2=3000; [lpb,lpa]=butter(8,f1/fs2); [bpb,bpa]=butter(8,[f1/fs2 f2/fs2]); [hpb,hpa]=butter(8,f2/fs2,'high'); [lph,f]=freqz(lpb,lpa,512,fs); [bph,f]=freqz(bpb,bpa,512,fs); [hph,f]=freqz(hpb,hpa,512,fs); plot(f,20*log10(abs(lph)+eps),'r-',f,20*log10(abs(bph)+eps),'g-',f,20*log10(abs(hph)+eps),'b-');