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The usual answer is a different way of signal processing.

So you need to do analyse both systems (including a lot of RTFM on both)  to find the differences in detail.

And it doesn't help to look at (or blame) only one system, if you want to compare two systems 😉


There are a lot of parameters to create a lot of spectra of different kind.

And Matlab and LabVIEW might use different default parameters if not defined.


Greetings from Germany

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

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Message 11 of 19

Hi GerdW,

find he attached VI in LV2017 version.


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Message 12 of 19

Hi sundas,


no, the VI still is saved for LV2018. Just renaming the file does not convert the LabVIEW version!

(Edit->Save for previous…)

Best regards,

using LV2016/2019/2021 on Win10/11+cRIO
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Message 13 of 19

I follow the same steps,

file > save for previous version > LabView version 17.0  and then i renamed it.

I will give it another try.

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Message 14 of 19

here is the attached code in LV2015 Version. I hope this will work as code conversion didnot work.


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Message 15 of 19

Hi sundas,


conversion worked this time…


The "spectral measurements" expects a waveform as input, so why do you convert your DDT data to a plain 1D array?

Why do you apply a moving average to the resulting spectrum?


What is the expected result after that Select function? One input gets a DDT (containing an array of signals) and the other just gets a 0 (scalar DBL)?


Why do you display just some samples from the filtered spectrum? How did you come up with these numbers (50-200)?

Best regards,

using LV2016/2019/2021 on Win10/11+cRIO
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Message 16 of 19

Its great that conversion works this time.

In some previous post i attached a folder which contains Matlab Code and 2 reference input data files. 

The purpose of my code is to detect the true input signal. In my case, i have to see the spectrum of signal and see its peak between 50 to 200 samples. 

For true signal this peak is always greater than 20; while for invalid input signal this peak is less than 20 in amplitude.

The Matlab file always give accurate results. But the same did not work in Labview. That's where i need your help. 


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Message 17 of 19

hi GerdW,

i am waiting for your positive response. 


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Message 18 of 19

Hi sundas,


This is what I get for your "test_3" data:


I just changed the FromDDT properties after that subtract node…

I still don't understand why you try to exactly pick 200 elements starting at index 50 from the filtered power spectrum?

What kind of data do those files contain? What does the (unused) first column contain?


Unfortunately I don't have the needed toolboxes installed in Matlab to run your m script…

Best regards,

using LV2016/2019/2021 on Win10/11+cRIO
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Message 19 of 19