%MatLAB Fourier transform example from Help File
%Modified to show both graphs in one plot.
%Steven Sahyun 141024

clear;
clf();

Fs = 1000;                    % Sampling frequency
T = 1/Fs;                     % Sample time
L = 10000;                     % Length of signal
t = (0:L-1)*T;                % Time vector
% Sum of a 50 Hz sinusoid and a 120 Hz sinusoid
x = 0.7*sin(2*pi*60*t) + 2*sin(2*pi*120*t) + sin(2*pi*300*t); 
noiseamp = 2; %Amplitude of noise term
y = x + noiseamp*randn(size(t));     % Sinusoids plus noise

%figure %create new plot window
subplot(2,1,1) %first subplot - this directs to a plot window with two plots (rows, columns, 1st plot)
plot(Fs*t(1:50),y(1:50))
title('Signal Corrupted with Zero-Mean Random Noise')
xlabel('time (milliseconds)')

NFFT = 2^nextpow2(L); % Next power of 2 from length of y
Y = fft(y,NFFT)/L;
f = Fs/2*linspace(0,1,NFFT/2+1);

% Plot single-sided amplitude spectrum.
subplot(2,1,2)%second subplot - this directs to the plot window with two plots (rows, columns, 2nd plot)
plot(f,2*abs(Y(1:NFFT/2+1))) 
title('Single-Sided Amplitude Spectrum of y(t)')
xlabel('Frequency (Hz)')
ylabel('|Y(f)|')