fftdemo19.m

Fs = 10;                        % Sampling frequency
Ts = 1/Fs;                      % Sampling period
N = 32;                         % Total number of samples
n = 0:N-1;                      % Samples
t = Ts*(n);                     % Sampled times
y = cos(2*pi*t) + .2*cos(2*pi*1.5*t);  % Discrete signal

N = length(y);                  % The new total number of samples
Y = fft(y);                     % The fft of the signal
df = 1/(N*Ts);                  % The frequency resolution
k = 0:N-1;                      % Frequency spectrum samples
f = k*df;                       % Frequency values at the k samples  

% Now lets make y length 128 by padding y with zeros
% p = "prime"
yp = y;
yp(length(y)+1:length(y)+96) = zeros(1,96);
Np = length(yp);                  % The new total number of samples
Yp = fft(yp);                     % The fft of the signal
dfp = 1/(Np*Ts);                  % The frequency resolution
kp = 0:Np-1;                      % Frequency spectrum samples
fp = kp*dfp;                      % Frequency values at the k samples   

% Plot the fft of the signal
figure
subplot(2,1,1), plot(fp,abs(Yp))
title('Spectrum of Zero-Padded Signal')
ylabel('|fft(y)|')
xlabel('Frequency (Hz)')
subplot(2,1,2), plot(f,abs(Y))
title('Spectrum of non Zero-Padded Signal')
ylabel('|fft(y)|')
xlabel('Frequency (Hz)')