第二题：
n=50; Wn=0.65,
b1=fir1(n,Wn,'high',boxcar(n+1)); [H,w]=freqz(b1,1,512,2); subplot(4,1,1);
plot(w,abs(H));grid;
title('矩形窗高通FIR数字滤波器'); b2=fir1(n,Wn,'high',hanning(n+1)); [H,w]=freqz(b2,1,512,2); subplot(4,1,2);
plot(w,abs(H));grid;
title('汉宁窗高通FIR数字滤波器'); b3=fir1(n,Wn,'high',hamming(n+1)); [H,w]=freqz(b3,1,512,2);
subplot(4,1,3);
plot(w,abs(H));grid;
title('海明窗高通FIR数字滤波器'); b4=fir1(n,Wn,'high',blackman(n+1)); [H,w]=freqz(b4,1,512,2);
subplot(4,1,4);
plot(w,abs(H));grid;
title('希拉克曼窗高通FIR数字滤波器');
运行结果：
矩形窗高通FIR数字滤波器21021021021000.10.20.30.40.50.60.70.80.9100.10.20.30.40.50.60.7希拉克曼窗高通FIR数字滤波器0.80.9100.10.20.30.40.50.60.7海明窗高通FIR数字滤波器0.80.9100.10.20.30.40.50.60.7汉宁窗高通FIR数字滤波器0.80.9120
第三题：
n=50;
Wn=[0.45,0.65];
b1=fir1(n,Wn,'bandpass',boxcar(n+1)); [H,w]=freqz(b1,1,512,2); subplot(4,1,1);
plot(w,abs(H));grid;
title('矩形窗带通FIR数字滤波器'); b2=fir1(n,Wn,'bandpass',hanning(n+1)); [H,w]=freqz(b2,1,512,2); subplot(4,1,2);
plot(w,abs(H));grid;
title('汉宁窗带通FIR数字滤波器'); b3=fir1(n,Wn,'bandpass',hamming(n+1)); [H,w]=freqz(b3,1,512,2);
subplot(4,1,3);
plot(w,abs(H));grid;
title('海明窗带通FIR数字滤波器'); b4=fir1(n,Wn,'bandpass',blackman(n+1)); [H,w]=freqz(b4,1,512,2);
subplot(4,1,4);
plot(w,abs(H));grid;
title('希拉克曼窗带通FIR数字滤波器');
运行结果：
矩形窗带通FIR数字滤波器21021021010.5000.10.20.30.40.50.60.70.80.9100.10.20.30.40.50.60.7希拉克曼窗带通FIR数字滤波器0.80.9100.10.20.30.40.50.60.7海明窗带通FIR数字滤波器0.80.9100.10.20.30.40.50.60.7汉宁窗带通FIR数字滤波器0.80.9121
第四题：
n=50;
Wn=[0.45,0.65];
b1=fir1(n,Wn,'stop',boxcar(n+1)); [H,w]=freqz(b1,1,512,2); subplot(4,1,1);
plot(w,abs(H));grid;
title('矩形窗带阻FIR数字滤波器'); b2=fir1(n,Wn,'stop',hanning(n+1)); [H,w]=freqz(b2,1,512,2); subplot(4,1,2);
plot(w,abs(H));grid;
title('汉宁窗带阻FIR数字滤波器'); b3=fir1(n,Wn,'stop',hamming(n+1)); [H,w]=freqz(b3,1,512,2);
subplot(4,1,3);
plot(w,abs(H));grid;
title('海明窗带阻FIR数字滤波器'); b4=fir1(n,Wn,'stop’,blackman(n+1)); [H,w]=freqz(b4,1,512,2);
subplot(4,1,4);
plot(w,abs(H));grid;
title('希拉克曼窗带阻FIR数字滤波器');
运行结果：
矩形窗带阻FIR数字滤波器21021021021000.10.20.30.40.50.60.70.80.9100.10.20.30.40.50.60.7希拉克曼窗带阻FIR数字滤波器0.80.9100.10.20.30.40.50.60.7海明窗带阻FIR数字滤波器0.80.9100.10.20.30.40.50.60.7汉宁窗带阻FIR数字滤波器0.80.91
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答：从低通、高通、带通、带阻的设计所得到的波形可以看出矩形窗的过渡带最窄，但是它的余振最大，布拉克曼窗的过渡带最长，几乎没有余振。
由于实际的DF在理想特性不连续的边缘处，H(w)产生一个过渡带。过渡带的宽度取决于窗口频谱的主瓣宽度.而余振取决于窗口频谱的旁瓣，旁瓣愈多，余振也越多。依据能量守恒，主瓣越宽必然导致旁瓣越小，主瓣越窄必然导致旁瓣越大。所以导致过渡带越宽余振越小，过渡带越窄余振越大。
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实验八：
实验（1）
源代码：
wp1=0.45*pi;wp2=0.65*pi; ws1=0.3*pi;ws2=0.75*pi; rp=1; rs=40; wp=[wp1,wp2]; ws=[ws1,ws2];
[n,wn]=buttord(wp/pi,ws/pi,rp,rs); [b,a]=butter(n,wn,'bandpass'); freqz(b,a);
得到图形为：
200Magnitude (dB)0-200-40000.10.20.30.40.50.60.70.8Normalized Frequency (?? rad/sample)0.910Phase (degrees)-500-1000-150000.10.20.30.40.50.60.70.8Normalized Frequency (?? rad/sample)0.91
源代码2：
i=0:0.001:0.1; x1=sin(600*pi*i); x2=sin(200*pi*i);
x3=sin(900*pi*i);
x=x1+x2+x3; y=filter(b,a,x);
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