10x or 20x in calculation the ADC sample sequence in decibel

[yakex]

hi,
I have adopt the ADS5560 for sampling, and the sample sequence is expresses as X in matlab. Then I want to calculate the power/energy spectrum in decibel, I have a problem whether to choose 20 or 10 as the multipy coefficient, i.e.,
20*log10(abs(fft(X)) or
10*log10(abs(fft(X))
thanks to all.
--yakex

 

[barry]

you want to use 10 if you're calculating power.

 

[MHanif]

hi,
I have adopt the ADS5560 for sampling, and the sample sequence is expresses as X in matlab. Then I want to calculate the power/energy spectrum in decibel, I have a problem whether to choose 20 or 10 as the multipy coefficient, i.e.,
20*log10(abs(fft(X)) or
10*log10(abs(fft(X))
thanks to all.
--yakex

PSD is abs(fft(X))^2 and 10log10(abs(fft(X))^2) gives result in dB which is 20log10(abs(fft(X)))

 

[yakex]

PSD is abs(fft(X))^2 and 10log10(abs(fft(X))^2) gives result in dB which is 20log10(abs(fft(X)))

thank you very much.