%  ex_04_09_1.m :  習題 4.9

clear all;

N=4096;
 f1=.1;
 fs=1;
 a1=5;
 w=2*pi/fs;
 x=a1*sin(w*f1*(0:N-1))+randn(1,N);
 
 % 應用FFT 求頻譜；
 figure('color','w')
 subplot(3,1,1);
 plot(x(1:N/100));
% title('x(n)');
 f=-0.5:1/N:0.5-1/N;
 X=fft(x); 
 %
 subplot(3,1,2);
 plot(f,fftshift(abs(X)));
 %title('|X(k)|');