例44设采样频率f=900Hz,设计n=9阶的 Butterworth的低通滤 波器,截止频率ω,=300Hz。与n=50阶的 Butterworth的 低通滤波器比较。(ex44.m) 解:(a)[ba]= butter(9,300/450); fretz(b,a2512,1000 (b)[ba]= butter(50,300/450); fretz(b,a512,1000 (b) Frequency(Hz) Frequency(Hz) -1000 1005010015020025030035040045050 -5000L 100150200250300350400450500 Frequency(Hz)例4.4 设采样频率fs=900Hz,设计n=9阶的Butterworth的低通滤 波器，截止频率ωn=300Hz。与n=50阶的Butterworth的 低通滤波器比较。(ex44.m) 解： (a) [b,a]=butter(9,300/450)；freqz(b,a,512,1000) (b) [b,a]=butter(50,300/450)；freqz(b,a,512,1000) (a) (b) 0 50 100 150 200 250 300 350 400 450 500 -80 -60 -40 -20 0 20 Frequency (Hz) Magnitude (dB) 0 50 100 150 200 250 300 350 400 450 500 -5000 -4000 -3000 -2000 -1000 0 Frequency (Hz) Phase (degrees) 0 50 100 150 200 250 300 350 400 450 500 -300 -200 -100 0 100 Frequency (Hz) Magnitude (dB) 0 50 100 150 200 250 300 350 400 450 500 -1000 -800 -600 -400 -200 0 Frequency (Hz) Phase (degrees)