% fft_noise.m
% 傅立葉變化示例
% 產(chǎn)生帶有噪聲的聲源信號(hào)，并提取離散信號(hào)
t=0:0.001:0.6;
% 噪聲信號(hào)的主頻為60Hz和150Hz
x=sin(2*pi*60*t)+sin(2*pi*150*t);
y=x+2*randn(size(t));
plot(1000*t(1:50),y(1:50))
title('Signal Corrupted with Zero-Mean Random Noise')
xlabel('time (ms)')
grid on;

% 進(jìn)行512點(diǎn)的快速傅立葉變換
Y=fft(y,512);
% 功率譜測(cè)量計(jì)算
Pyy=Y.* conj(Y)/512;
f=1000*(0:256)/512;
% 繪制頻譜圖形
figure;
plot(f,Pyy(1:257))
title('Frequency content of y')
xlabel('frequency (Hz)')
grid on;