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FFT and Third octave discrepancy - Sound and Vibration

Hello all, I need some help with a problem that Im having. Im currently analyzing a calibration signal and when I perform the FFT signal analysis I find a peak with amplitud 93.1dB @998,66Hz and 2 peak sides of aprox. 87dB (marked in the picture attached). Then i performed a Third octave analysis and I found that the Band related to 1000Hz has an amplitude of 93.1dB. My question is: just the sum of these 3 bins  gives me an amplitude of aprox 99dB, why the amplitude of the band is 93.1dB? What Im misunderstanding? Thank you so much for your help.

Regards,

Alan

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Hello alanesco,

 

Only a few questions about application, I'm curious about the sampling rate that are you using, ¿what hardware and sampling rate are you using?

 

Best regards.

David P.
National Instruments
Applications Engineer
www.ni.com/soporte
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