fft and automatic filter

[madness]

Thank you for the answer.

Can you just indicate me where to find the vi, becasuse my labview is in french.
May I find it in the examples? control panel???

Thank you in advance.

[DFGray]

Both of these VIs, in the English version, are in Analyze>>Waveform Measurements menu. I have attached a LabVIEW 7.0 screenshot.

[madness]

thanks DFgray.

So, I have the labview full version.
the problem is that
First : I dont have a waveform, but a 2D array that I wire to a graph. How to convert my datas to a waveform...
second : I Dont want to scan just One frequency but 5% before and 5% after the frequency.
Then the detection have to be automatic : if the value of the data if higher than the threshold, put the data to the value of the threshlod.

Can you help me on those two points.

Please give in mind that the datas are big, and that the vi dont have to take to much memory.

Regards

[DFGray]

Before I try to give you much more advice, I will probably need a better description of your data. The example you posted has a 1D waveform, not a 2D. It is easy to convert this to a waveform data type using the primitives in the waveform palette (Build Waveform). The VIs I mentioned will compensate for the peak broadening you get with FFTs, but I believe they also subtract the entire peak. You will need to reconstruct the background after the filter using linear or polynomial interpolation. I strongly urge you to read Numerical Recipes in C on the subject. If nothing else, go to amazon.com and browse through the section on optimal (wiener) filtering.

As for large data sets, that usually introduces complexity. Check out the tutorial Managing Large Data Sets in LabVIEW for general hints. It does not specifically cover FFTs. How big is big? 10kBytes? 10MBytes? 10GBytes? You can pretty easily do fourier filtering in chunks. Follow the hints given in Numerical Recipes.

Good luck and post more details of your exact data form (and example code) if you need more help.