Matlab操作实验报告

数字信号处理Matlab操作实验报告

实验一

1.1 实验要求

指定一序列进行以下操作：补零、重复原序列本身，分别画出对应幅度谱

1.2 程序设计 (1)末尾补零法

>> x=ones(1,16) x =

Columns 1 through 13

1 1 1 1 1 1 1 1 1 1 1 1

Columns 14 through 16

1 1 1 >> figure;stem(x)

10.9

0.80.70.60.50.40.30.20.100

2

4

6

8

10

12

14

16

>> y=[ones(1,16),zeros(1,16)] y =

1

Columns 1 through 13

1 1 1 1 1 1 1 1 1 1 1 1 1

Columns 14 through 26

1 1 1 0 0 0 0 0 0 0 0 0 0

Columns 27 through 32

0 0 0 0 0 0 >> figure;stem(y)

10.90.80.70.60.50.40.30.20.10

>> y=fft(x,32);

>> figure;stem(abs(y))

1614121086420

(2)重复原序列本身

>> x=ones(1,16); >> figure;stem(x)

10.9

0.80.70.60.50.40.30.20.100

2

4

6

8

10

12

14

16

>> y=fft(x,32) y =

Columns 1 through 4

16.0000 1.0000 -10.1532i 0 1.0000 - 3.2966i

Columns 5 through 8

0 1.0000 - 1.8709i 0 1.0000 - 1.2185i

Columns 9 through 12

0 1.0000 - 0.8207i 0 1.0000 - 0.5345i

Columns 13 through 16

0 1.0000 - 0.3033i 0 1.0000 - 0.0985i

Columns 17 through 20

0 1.0000 + 0.0985i 0 1.0000 + 0.3033i

Columns 21 through 24

0 1.0000 + 0.5345i 0 1.0000 + 0.8207i

Columns 25 through 28

0 1.0000 + 1.2185i 0 1.0000 + 1.8709i

Columns 29 through 32

0 1.0000 + 3.2966i 0 1.0000 +10.1532i >> figure;stem(y)

15

10

5

-5

-10

-15

05101520253035

>> figure;stem(abs(y))

1614121086420

实验二

2.1实验要求

f1 10Hz,f2 100Hz,fs 500Hzx(t) cos(2 f1t) cos(2 f2t) x1(t) x2(t)

设计一个巴特沃斯型和切比雪夫Ⅰ型数字低通滤波器，把x1(t)提取出来，要求通带衰减小于1dB，阻带衰减大于15 dB。画出所设计DF的频响，分析滤波前后信号的频谱

2.2 实验设计 （1）巴特沃斯型

设置通带截止频率fc=35Hz,，阻带的起始频率fs=40Hz. >> Fs=500; >> T=1/Fs; >> fc=35; >> fs=50;

>> wc=fc*2*pi*T; >> ws=fs*2*pi*T; >> Wc=wc/pi; >> Ws=ws/pi;

>> [N,W]=buttord(Wc,Ws,1,15) N =

7 W =

0.1586

>> [b,a]=butter(N,W) b =

1.0e-003 *

Columns 1 through 7

0.0222 0.1555 0.4664 0.7773 0.7773 0.4664 0.1555

Column 8

0.0222 a =

Columns 1 through 7

1.0000 -4.7635 9.9850 -11.8788 8.6336 -3.8245 0.9543

Column 8

-0.1033

>> y=freqz(b,a);

>> f=0:Fs/2/512:Fs/2-Fs/2/512; >> plot(f,abs(y))

1.4

1.2

1

0.8

0.6

0.4

0.2

050100150200250

（2）切比雪夫I型滤波器

设置通带截止频率fc=40Hz,，阻带的起始频率fs=50Hz. >> Fs=500; >> T=1/Fs; >> fc=40; >> fs=50;

>> wc=fc*2*pi*T;

>> ws=fs*2*pi*T; >> Wc=wc/pi; >> Ws=ws/pi;

>> [N,W]=cheb1ord(Wc,Ws,1,15) N =

5 W =

0.1600

>> [b,a]=cheby1(N,1,W) b =

1.0e-003 *

0.1000 0.4998 0.9997 0.9997 0.4998 0.1000 a =

1.0000 -4.2364 7.4629 -6.8073 3.2088 -0.6249

>> y=freqz(b,a);

>> f=0:Fs/2/512:Fs/2-Fs/2/512; >> plot(f,abs(y))

10.9

0.80.70.60.50.40.30.20.100

50

100

150

200

250

2.3 实验分析 （1）最初波形

10.5

0-0.5-1

10.5

0-0.5-1

00.510510

21

0-1-2

00.10.20.30.40.50.60.70.80.91

(从上至下，分别对应x1(t),x2(t),以及x(t)) >> f1=10; >> f2=100; >> Fs=500; >> t=(1:500)/Fs;

>> x1=cos(2*pi*f1*t); >> x2=cos(2*pi*f2*t); >> x=x1+x2;

>> subplot(2,2,1);t=(1:500)/Fs;plot(t,x1); >> subplot(2,2,2);t=(1:500)/Fs;plot(t,x2);

>> subplot(2,1,2);t=(1:500)/Fs;plot(t,x);

（2）解调波形

>> Y=filter(b,a,x);

>> subplot(1,2,1);plot(t,x1); >> subplot(1,2,2);plot(t,Y);

10.8

0.60.40.2

0-0.2-0.4-0.6-0.8

-1

1

0.5

-0.5

-1

-1.5

右为经过巴特沃斯滤波器后恢复的波形

1

0.80.60.40.20-0.2-0.4-0.6-0.8-1

10.80.60.40.20-0.2-0.4-0.6-0.8-1

右为经过切比雪夫1型滤波器恢复后的波形

可以看出切比雪夫1型滤波器设计的优于巴特沃斯滤波器，主要两滤波的通带截止频率与阻带的起始频率不同，影响滤波特性。无论是哪种滤波器，对应的滤波后的幅度谱的条数减少，减少一半。 >> S=fft(x,512);

>> l=(0:255)/256*(Fs/2); >> s=fft(Y,512); >> A=fft(x1,512);

>> subplot(2,2,1);plot(l,abs(S(1:256))); >> subplot(2,2,2);plot(l,abs(s(1:256))); >> subplot(2,1,2);plot(l,abs(A(1:256)));

250200

1501005000

100

200

300

250200

1501005000

100

200

300

250200

1501005000

50

100

150

200

250

（1、x的幅度谱 …… 此处隐藏：1169字，全部文档内容请下载后查看。喜欢就下载吧 ……