clc,clear all,close all;
n=[0:1:999];
xn=10*cos(0.2*pi*n)+1.2*cos(0.25*pi*n)+4.6*cos(0.6328*pi*n);    %先定義一個(gè)長序列，處理時(shí)再截取

%(11111111)用漢明窗截獲加隨機(jī)信號(hào)進(jìn)行頻譜分析%%%%%%%%%%%%%%%%%%%%%%%%%
%32點(diǎn)的DFT
w1=hamming(32);           %生成一個(gè)32點(diǎn)的漢明窗，為列矢量
xn1=xn(1:32);             %截取xn的前32個(gè)點(diǎn)
r1=randn(size(w1));        %產(chǎn)生隨機(jī)信號(hào)
xn11=(xn1+0.3*r1').*w1';   %將截取的序列和矩形窗相乘
X1=dft(xn11,32);          %做32點(diǎn)的DFT，其中DFT函數(shù)已定義
subplot(2,2,1);
plot([0:1:31],X1);
xlabel('n=0:31 32-point dft');
ylabel('the result of dft --w');

%64點(diǎn)的DFT%%%%%%%%%%%%%%%%%%%%%%%%%
w2=hamming(64);
xn2=xn(1:64);
r2=randn(size(w2));
xn22=(xn2+0.3*r2').*w2';
X2=dft(xn22,64);
%subplot(2,2,2);
%plot([0:1:63],X2);
xlabel('n=0:63 64-point dft');
ylabel('dft result --w');

%128點(diǎn)DFT%%%%%%%%%%%%%%%%%%%%%%%%%
w3=hamming(128);
xn3=xn(1:128);
r3=randn(size(w3));
xn33=(xn3+0.3*r3').*w3';
X3=dft(xn33,128);
%subplot(2,2,3);
%plot([0:1:127],X3);
xlabel('n=0:127 128-point dft');
ylabel('dft result --w');

%256點(diǎn)DFT%%%%%%%%%%%%%%%%%%%%%%%%%
w4=rectwin(256);
xn4=xn(1:256);
xn44=xn4.*w4';
X4=dft(xn44,256);
%subplot(2,2,4);
%plot([0:1:255],X4);
xlabel('n=0:255 256-point dft');
ylabel('dft result --w');