apply "windowing" to already smapled data?

[fenny]

Hi, There:

I have a question about applying "windowing" to already sampled data.

I have had teh tutorial of NI about windowing data, seems that it is about applying windowing to the data at the moment of smapling.

I wnat to know if it is Ok to apply windowing after the data has alreday been smapled?

And How can I personalize the window function for my data?

say " the width" of the window?

seems that I can not chnage the width of the window.

BTW, my data is impulse response data.


thanks for your sincere help!

Fenny

[THailey3]

Hi Fenny,

As far as personalizing the window function, what window function are you referring to? Are you referring to the window functions in the Analyze->Signal Processing->Windows palette? If so, you can dig into the VIs to see how they are implemented in code. If you dig deep enough, you will get to a dll call (that you can't modify), but there are coefficients in LabVIEW code that you can tweak. As far as it being "ok" to apply windowing on sampled data, I don't see why it wouldn't be, but I can't say I'm the most experienced in that subject.

Good luck,

[rpursley8]

It is OK to window existing data. You can think of your exising data as a signal windowed with a square window and you are just applying another one. If you want a window smaller than your data set, then you will create the window of the size you want and then pad it with zeros on one or both sides to position it where you want it in the data set.

[fenny]

Yes, I want to apply the window function from the window pallete to the existing data.
The problem is when I dig into the vi, how can I modify the paremeters to make a window suitable for my apllication.
When I dig into Hanning window, it seems that the coefficients are existing constant paremeters selected from case structure.

[rpursley8]

Most of these windows are defined by their coefficients. A Hanning window is a Hanning window due to the values of the coefficients. What parameters do you want to modify to customize your own window? Most windows are used to minimize discontinuites due to finite sampling of the data. What are you using a window for?

As I mentioned before, if you want a window of a certain width, then create an array of all ones of your desired 'width' and apply the window function to this array and you will have your of desired 'width' and then pad zeros around it to make it the same size as your sampled signal and place it where you want it to be.

As for changing the shape of the window, there are a couple with an input the modifies the shape of the window, but most have a well defined shape optimized for specific applications.