Which spectrum (pwelch vs. spectrumAnalyzer) is correct?

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Jay 2025-6-10

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https://ww2.mathworks.cn/matlabcentral/answers/2177685-which-spectrum-pwelch-vs-spectrumanalyzer-is-correct

评论： Jay 2025-6-12

I have two data which I want to see difference in frequency domain. I tried with pwelch function which shows they are quite close and no meaningful difference. Then I checked the spectrum with spectrumAnalyzer toolbox. The spectrum with the spectrumAnalyzer shows difference although they are rough. Perhaps I need to play around with RBW and VBW?

My question is which spectrum am I supposed to rely on?I also try with FFT which is quite similar with pwelch.

The first plot is from pwelch.

Then the same data with spectrumAnalyzer toolbox without changing parameter. Note that I don't know how to overlay multiple plots in a single spectrumAnalyzer which made me put two captures side by side.

Which one is correct and how to make the same like the other?

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Abhipsa 2025-6-12

Could you please provide the set of parameters and their values used?

Jay 2025-6-12

Thanks @Abhipsa for the reply.

The original plots were from default settings, meaning I didn't change or set any parameter. I overlayed two plots with spectrum analyzer and changed RBW and VBW to 3kHz. Now, it seems that pwelch and spectrum analyzer plots are quite close (updated spectrum analyer plot in the original post). So my guess is that previous separate spectrum analyzer plots had their own default settings for optimal visualization which caused different waveforms in the separate screens. However, it seems to be not the case. Now I can say pwelch and spectrum analyzer are showing the same plot.

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