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Filter the data and then do an inverse FFT

Hi everyone,

 

I know this subject has ever been treated but it's not been solved so here's my question :

 

First I want to make an FFT on datas. Then I want to filter values (replacing the values I want to filter by 0) and finally make an inverse FFT to get back the time signal without the high frequencies.
Now my question is, how do I modify complex datas or how do I make my modified array acceptable for the inverse FFT vi ? 

 

Thanks a lot 😉

David

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Have you done any coding you can post? Are you familiar with how the output from the FFT is organized? It took me some time to get grasp on FFT I have to admit


Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)
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Hi ! here's a little bit of coding i've done. I tried to get the real part to see what it was like but I just can't get it ! How do you get from that a frequency/amplitude spectrum ? 

 

 

complex.JPG

Message Edité par David F le 06-04-2009 02:58 AM
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I think your problem is that you need some more FFT information. You are uncertain on how the output from the FFT VI is organized. Or more specific how to map the array content to different frequencies 😉

I suggest you read this http://zone.ni.com/devzone/cda/tut/p/id/4278, and this http://zone.ni.com/devzone/cda/tut/p/id/4541. In the last one they used an older labview version. Some of the functions mentioned has minor changes in newer Labview versions. But the theory still apply

If you can answer this question I can help you some more.

If I sample a 5Hz sine wave with 1Khz sample rate for 1 second, and then perform a FFT, at which array indexes will I find information about the 5Hz sine wave



Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)
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