Difference of FFT Spectrum and Power Spectrum

[jamison.suade]

Hi all,

I'm confused on what actually is the difference between the FFT Spectrum and Power Spectrum?

I've tried simulating a sine signal, and perform the FFT spectrum and Power Spectrum. They both show the same graph.

[jamison.suade]

Anyone who has an idea on this?

[altenbach]

I don't recognize your transform subVIs. Are they from a toolkit or from an ancient LabVIEW version? Can you attach your VI?

In any case, the FFT also contains phase information, but you are currently only looking at the magnitude. There is a second output for phase for the FFT case!

Instead, use the subVI that produces the real and imaginary parts, then change the phase of the input signal and see what happens e.g. to the real or imaginary part.

[ben64]

Where are the FFT Spectrum and Power SpectrumVIs are from? Also, the Sine Waveform.vi generates a pure 2k single tone, How are the noise, 3k and 4k tones generated?

Ben64

[jamison.suade]

The FFT Spectrum and Power Spectrum are located under Sound and Vibration --> Stimulus - Response Test --> Baseband FFT

[altenbach]

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@jamison.suade wrote:

The FFT Spectrum and Power Spectrum are located under Sound and Vibration --> Stimulus - Response Test --> Baseband FFT

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That's not plain LabVIEW, but from a toolkit I guess.

[jmoody]

While they're fairly similar, you can see some differences if you look at the inputs and outputs.  For instance, you can also see the phase of your FFT spectrum with the FFT Spectrum (mag-phase) VI.  You can also switch the Power Spectrum to/from dB with its boolean input, though you can also do that with a unit conversion VI down the line on either of them.

[Mrwang]

what your problem solved?I was plagued by the problem！

[altenbach]

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@Mrwang wrote:

what your problem solved?I was plagued by the problem！

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We found that there was no problem. Please explain what you still perceive as problem.

[Mrwang]

I'm sorry, I carefully read your previous explanation, understand! Can I ask your other question? I'm doing noise analysis, very confused!