Alias when Fstop > Fs/2 in matlab

matlab alias

Hello Sir/Madam,

If filter fstop > fs/2, i should see alias.

How can i simulate this alias in matlab? Can anyone give some suggestion here?

Thanks.

aliasing matlab code

Do u want to simulate the alising effect and show ,...as in a presentation or somthin lik tat

matlab example aliasing

Hi tibm,

Yes. I would like to see the alias effect if we don't design the filter well where the stopband > fs/2.

Do you have any idea? THanks.

pi = fs/2

Aliasing Example

The program below demonstrates this problem graphically. We simulate sampling
two sinusoids, 2 cos(2Π100t +Π/3) and 2 cos(2Π600t +Π/3), at 500 samples/second.
They are given the same magnitude and phase for a reason: the program shows that the sampled versions are identical.

%
% Example of aliasing with
% 2 cos(2 pi 100 t + pi/3)
% and 2 cos(2 pi 600 t + pi/3)
%
% if these are sampled at 500 samples/sec,
% then the sampled versions are identical!
%
freq = 100; % example frequency
phase = pi/3; % example phase
mag = 2; % example magnitude
fs = 500; % sampling frequency
Ts = 1/fs; % sampling period
k = 1; % number of repetitions
num_points = 200; % How many points to use
% 200 makes it look smooth
num_samples = 11; % How many samples to simulate reading
% 11 puts "sampled" under "analog"
step = 2/(freq*num_points); % get a nice step size
t = 0:step:2*(1/freq); % "time"
n = 0:num_samples-1; % sample index
% x and y are simulated analog functions
x = mag*cos(2*pi*freq*t + phase);
y = mag*cos(2*pi*(freq+k*fs)*t + phase);
% x2 and y2 are simulated sampled version of x and y
x2(n+1) = mag*cos(2*pi*freq*n*Ts + phase);
y2(n+1) = mag*cos(2*pi*(freq+k*fs)*n*Ts + phase);


Both x2 and y2 have the same values. To show the simulated sampled versions,
the following code plots both, and generates Figure 5.2.

% Plot the "analog" signals
subplot(2,1,1);
plot(t, x, 'r.-', t, y,'b-');
my_title = sprintf('Simulated analog signals, x=dots y=solid');

figure 5.2:


By the way: this is not my own program. I found it in the following book:

Digital Signal Processing using Matlab and Wavelets

By: Michael Weeks ©2007

matlab alias signal

Hi Aya2002,

Thanks for your reply.

I think your code is more on demonstrate the concept of alias.

What i am looking forward is a matlab code to show alias happen for filtered signal if the digital filter have Fstop>Fs/2.

Thanks.