FFT power spectrum formula

[pbsalunkhe]

Hi

Can anyone please tell me the formula used in the LabView for calculation of FFT power spectrum in decibles?

Thanks in advance

Pramod

[Mathan]

quick search

search the forum and post if any specific help needed.

[Coq_Rouge]

What is your problem. Do you only have labview base, or is it something else.

[pbsalunkhe]

Hi

I have already searched but didn't got the exact info.

In linear scale,         power spectrum=fft(X)^2  where X is time series.

In decibles scale,    power spectrum=10*log10(fft(X)^2).

I am not sure whether the above formula in decibles is correct.  

I used LabView for spectral analysis. I need to do the wavelet analysis using Matlab. In Matlab, I will require the subplot of fft power spectrum. I can do that if I know the exact formula in decibles.

I will appreciate if someone will tell me.

Thanks

Pramod

[Coq_Rouge]

The output from the power spectrum is (amplitude value(rms)^2)/2 for non DC values and DC^2 . To find rms value of a sinus wave you divide  with square root(2). The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity) relative to a specified or implied reference level. Take a look at this site for more. http://www.sengpielaudio.com/calculator-db-volt.htm

[Hayk]

Hello!

Have a look links below:

http://www.ni.com/white-paper/4278/en/ 

https://www.ni.com/docs/en-US/bundle/labwindows-cvi/page/advancedanalysisconcepts/power_spect.html

http://www.ni.com/product-documentation/54619/en/ 

Formulas are written both for power spectrum and amplitude spectrum.