how to compute the RMS dB(A) value from an acoustic signal in a spectrum ?

i have processed the .wav file and plotted the db(a) vs freqyncy data. But the RMS value using the in-built function of matlab returns a different value compared to Siemens Test center that i used to proess the audio file.

i Believe there is a difference between the rms formulas used in both the cases.

can anybody help me ?

Answer 1

[Jimmy Lapierre]

It might just be a matter of scaling. For example, if there is a microphone involved, you may need to calibrate for that if the other software is.