t = 0:0.001:0.6;
x = sin(2*pi*50*t)+sin(2*pi*120*t);
y = x + 2*randn(size(t));
subplot(1,2,1)
plot(1000*t(1:50),y(1:50))
title('Signal Corrupted with Zero-Mean Random Noise')
xlabel('time (milliseconds)')



 


Y = fft(y,512);


Pyy = Y.* conj(Y) / 512;



f = 1000*(0:256)/512;
subplot(1,2,2)
plot(f,Pyy(1:257))
title('Frequency content of y')
xlabel('frequency (Hz)')