anti-aliasing filter after sampling

can I applied an anti-aliasing filter to the signal after sampling; and how to do this

Answer 1

[Star Strider]

As a general rule, anti-aliasing filters are implemented in hardware (as analogue filters) before sampling. An aliased signal in your sampled signal will always be part of it.

[mouh nyquist]

thank you a lot for your answer , but can I use a anti-aliasing filter after sampling (because I can't used an analogue filters in my laboratory)

[Star Strider]

The problem with not using an anti-aliasing filter in hardware is that signals above the Nyquist frequency of your digitising hardware will be included in your sampled signal. You cannot then filter them out. A discrete anti-aliasing filter will be a broadband filter including everything up to the Nyquist frequency — and that would be your entire sampled signal. It would therefore serve no purpose to filter it.

[mouh nyquist]

thank you a lot again; I have a Dspace 1104 , can I use an anti-aliasing filter in matlab (simulink program)

[Star Strider]

My pleasure.

I have no idea what a ‘Dspace 1104’ is or what it can do.

Anything you can implement in Simulink is essentially the same as the rest of MATLAB, with the same restrictions. What I said earlier applies to Simulink as well.

A suitable anti-aliasing hardware filter is fairly easy to design and construct using a single op-amp. You can probably find the instructions and design equations online. The op-amp and design of course depend on the frequency you are filtering.

[mouh nyquist]

thank you a lot;

the Dspace 1104 is for the data acquisition; and in the simulation results the anti-aliasing filters is used ?

[Star Strider]

My pleasure.

Does it have its own anti-aliasing filters? If it is a DAQ board, it might.

[mouh nyquist]

thank you a lot for your help ; now I understand what anti-aliasing filters mean :)

[Star Strider]

My pleasure!