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I'm new to signal processing and I'm working with librosa library quite a bit.

  1. I would like to know what is the information that is returned by librosa.load function when I read a audio(.wav) file using it. Is it the instantaneous sound pressure in pa? or the just the instantaneous amplitude of the sound signal with no unit?

  2. How can I use this information to calculate the SPL(no-weigting) of the signal ?

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Is it the instantaneous sound pressure in pa?

How would a piece of software know about sound pressure? What it gets is the digitized voltage from a microphone, with zero information about the physical sensitivity of that microphone.

or the just the instantaneous amplitude of the sound signal with no unit?

Exactly! :)

How can I use this information to calculate the SPL(no-weigting) of the signal?

Calibrate your recording setup with a sound source of known power. That's the only way short of buying an expensive calibrated measurement microphone, amplifier, digitizer. But then, there will be little need for librosa.

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  • $\begingroup$ Does this instantaneous amplitude represent the change in atmospheric pressure created by the sound source(s) while recording? $\endgroup$
    – thileepan
    May 24, 2020 at 15:11
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    $\begingroup$ it's proportional to the instantaneous pressure. $\endgroup$
    – Marcus Müller
    May 24, 2020 at 15:18
  • $\begingroup$ So, can the instantaneous pressure be used with the reference atmospheric pressure(20e-6) to calculate the relevant SPL? $\endgroup$
    – thileepan
    May 24, 2020 at 15:23
  • $\begingroup$ no. constant pressure doesn't contribute to SPL. $\endgroup$
    – Marcus Müller
    May 24, 2020 at 15:25
  • $\begingroup$ Doesn't the instantaneous pressure keep varying(possibly) sample-to-sample? Why do you say this is constant pressure then? $\endgroup$
    – thileepan
    May 24, 2020 at 15:28

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