第四次数字信号处理实验.docx
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第四次数字信号处理实验
第六章：
1:
Wp=2*pi*400;Ws=2*pi*600;
ap=0.3;as=60;Fs=1000;
[N,Wc]=buttord（Wp,Ws,ap,as,'s'）;%求阶数N和3dB截止频率Wc
[Z,P,K]=buttap（N）;
[A,B,C,D]=zp2ss（Z,P,K）;%将模拟滤波器的零、极点形式转换为状态空间形式
[At,Bt,Ct,Dt]=lp2lp（A,B,C,D,Wc）;%去归一化
[num1,den1]=ss2tf（At,Bt,Ct,Dt）;%由状态空间形式转换为模拟系统函数的系数
[num2,den2]=impinvar（num1,den1,Fs）%求数字系统函数
[H,W]=freqz（num2,den2）;
plot（W*Fs/2/pi,abs（H））;grid;
xlabel（'频率/Hz'）;
ylabel（'幅值'）;
Warning:
Theoutputisnotcorrect/robust.
CoeffsofB（s）/A（s）arereal,butB（z）/A（z）hascomplexcoeffs.
Probablecauseisrootingofhigh-orderrepeatedpolesinA（s）.
>Inimpinvarat122
num2=
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0.00000
den2=
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0.0000-0.0000
2:
wp=0.2;ws=0.6;
ap=3;as=40;%注意wp，ws是关于π的归一化的值
[N,wc]=buttord（wp,ws,ap,as）%求数字滤波器阶数N和3dB截止频率wc
[B,A]=butter（N,wc）%调用butter计算数字滤波器系统函数系数向量B和A
[H,lW]=freqz（B,A）;
plot（W*Fs/2/pi,abs（H））;grid;
xlabel（'频率/Hz'）;
ylabel（'幅值'）;
N=
4
wc=
0.2613
B=
0.01180.04730.07090.04730.0118
A=
1.0000-1.87781.6214-0.66300.1087
第七章
1:
passrad=2*pi*100/1000;
w1=boxcar（81）;%矩形窗
w2=triang（81）;%三角窗
w3=hanning（81）;%汉宁窗
w4=hamming（81）;%矩形窗
n=1:
1:
81;
hd=sin（passrad*（n-41））./（pi*（n-41））;
hd（41）=passrad/pi;
h1=hd.*rot90（w1）;
h2=hd.*rot90（w2）;
h3=hd.*rot90（w3）;
h4=hd.*rot90（w4）;
[MAG1,RAD]=freqz（h1）;
[MAG2,RAD]=freqz（h2）;
[MAG3,RAD]=freqz（h3）;
[MAG4,RAD]=freqz（h4）;
subplot（2,2,1）;
plot（RAD,20*log10（abs（MAG1）））;
gridon;
subplot（2,2,2）;
plot（RAD,20*log10（abs（MAG2）））;
gridon;
subplot（2,2,3）;
plot（RAD,20*log10（abs（MAG3）））;
gridon;
subplot（2,2,4）;
plot（RAD,20*log10（abs（MAG4）））;
gridon;
2:
fp=2000;fs=3000;Fs=10000;
wp=2*pi*fp/Fs;ws=2*pi*fs/Fs;
B=ws-wp;
N=ceil（8*pi/B）;
wc=（wp+B/2）/pi;
hn=fir1（N-1,wc）;
M=1024;
Hk=fft（hn,M）;
n=0:
N-1;
subplot（2,1,1）;
stem（n,hn,'.'）;
xlabel（'n'）;ylabel（'h（n）'）;
gridon;
k=1:
M/2+1;
w=2*（0:
M/2）/M
subplot（2,1,2）;
plot（w,20*log10（abs（Hk（k））））;
axis（[0,1,-100,5]）;
xlabel（'w/pi'）;ylabel（'20lg∣H（w）∣'）;
gridon;
w=
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3:
delta=0.4*pi;
wc=0.2*pi;
as=40;
n=ceil（8*pi/delta）+1;
win=hamming（n）;%哈明窗
h=fir1（n-1,wc/pi,win）;
omega=linspace（0,pi,512）;
mag=freqz（h,[1],omega）;
magdb=20*log10（abs（mag））;
plot（omega,magdb）;
axis（[0pi-1000]）;
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