實(shí)驗(yàn)三 離散傅里葉變換

1、實(shí)驗(yàn)三 離散傅里葉變換23320078104194 07通信工程 戴文一·實(shí)驗(yàn)?zāi)康?·掌握離散傅里葉級數(shù)2·掌握DFT變換3·掌握DFT特性4·掌握利用DFT計(jì)算線性卷積5·掌握快速傅里葉變換（FFT）二·實(shí)驗(yàn)原理1·離散傅里葉級數(shù)2·離散傅里葉變換3·DFT特性4·利用DFT計(jì)算線性卷積5·快速傅里葉變換三·實(shí)驗(yàn)內(nèi)容1（2）. clear all;xn=1,2,3,0Xk=dfs(xn,4)運(yùn)行結(jié)果Xk = 6.0000 -2.0000 - 2.0000i 2.0

2、000 + 0.0000i -2.0000 + 2.0000i2_2.clear all;x=1,1,1,1,1,1;a=dft(x,6)figure(1);subplot(2,1,1);stem(abs(a)subplot(2,1,2);stem(angle(a)figure(2);b=idft(a,6)subplot(2,1,1);stem(abs(b)subplot(2,1,2);stem(angle(b)2（3）_a.n=0:10;a=dft(x,11);figure(1);subplot(2,1,1);stem(abs(a)subplot(2,1,2);stem(angle(a)2（

3、3）_b.n=0:10;a=x,zeros(1,90);figure(1);stem(a)y=dft(a,101);figure(2);subplot(2,1,1);stem(abs(y)subplot(2,1,2);stem(angle(y)figure(3);yy=fft(a,101);subplot(2,1,1);stem(abs(yy)subplot(2,1,2);stem(angle(yy)2（3）_c.n=0:500;a=dft(x,501);figure(1);subplot(2,1,1);stem(abs(a)subplot(2,1,2);stem(angle(a)3_1.n=

4、0:10;x=10*(0.8).n;figure(1);stem(x)figure(2);a=cirshftt(x,15,11);stem(a)3(2). x1=1,2,2;x2=1,2,5,4;y1 = circonvt(x1,x2,5)x1=1,2,2;x2=1,2,5,4;y2 = circonvt(x1,x2,6)4.x=1,2,3,4,5,6,7,8,9,10;h=1,0,-1;figure(1);subplot(2,1,1);stem(x)subplot(2,1,2);stem(h); b=ovrlpsav(x,h,4);figure(2);subplot(2,1,1);stem(

5、abs(b)subplot(2,1,2);stem(angle(b)5.1n=0:44;a=fft(x,45);stem(abs(a)5.2w=randn(1,64);a=fft(x,64);stem(abs(a)圖形： 2_22_3a 2_3b 2_3c345四·思考題1·clear all;clc;x,fs,bits=wavread('ding');Sound(x,fs,bits);n=0:999;t=0.1*n;y=fft(x);a=size(x) %數(shù)據(jù)量subplot(211);stem(abs(x)subplot(212);stem(abs(y)

6、2·clear all;clc;noise=randn(1,N);x=cos(100*pi*t)+cos(240*pi*t);x1=cos(100*pi*t)+cos(240*pi*t)+noise;y=fft(x);y1=fft(x1);subplot(2,1,1);stem(n,abs(y)title('無噪音幅值譜')subplot(2,1,2);stem(n,abs(y1)title('有噪音幅值譜')3·clear all;clc;x=2*sin(2*pi*20.*t)+5*cos(2*pi*30.*t)+sin(2*pi*45.*

7、t);y=fft(x,N);subplot(2,1,1);stem(x)title('原信號')subplot(2,1,2);stem(abs(y)title('DFT變換后的信號')4·clear all;clc;x=2*sin(2*pi*50.*t)+1.2*randn(size(t);y=fft(x,N);stem(abs(y)title('FFT變換后的信號')5·clear all;clc;load sunspot.dat year = sunspot(:,1); wolfer = sunspot(:,2); figure(1)plot(year,wolfer) title('Sunspot Data')Y = fft(wolfer);N = length(Y); Y(1) = ; power = abs(Y(1:N/2).2; nyquist = 1/2; freq = (1:N/2)/(N/2)*nyquist; figure(2)plot(freq,power), grid on xlabel('cycles/year')