Hey fancy folk,
So my goal is to get the sound pressure level (SPL) from the Sound and Vib toolkit. I need the SPL for the third octave bands of my incoming time signal. From my understanding this the SPL is a ratio of absolute sound pressure to a reference level (20 uPa). My current vi's logic is: acquire the data via DAQmx, send to a windowing vi, send to the octave analysis vi, then to a weighting vi, then to an octave graph. My DAQmx channel converts the voltage read to Pa (I have verified the gain of my microphone via a sound calibrator).
If I understand sound measurements correctly, the sound power level is like a 60W light bulb and the SPL is the brightness. IE, sound power is a known value (such a a speaker's output) and the SPL is the "power level" in regards to a listener (such as brightness to the observer for that 60W light bulb).
From my understanding, the sound and vibe toolkit likes to keep things with the term EU, which they have as a general catch all for the different units of data one can have. So since I'm reading my data in Pa, the EU should be Pa. When acquiring the signal from DAQmx, I should be getting that sound pressure in regards to the listener, meaning that the data should be in SPL.
My question is, what does the third octave VI analysis actually output data in? If the boolean "dB on" is true (which it is), this gives me dB EU rms (dB Engineering Units rms). That means that I should have my data being output as dB Pa rms. If thats the case, is that the same thing as the dB SPL? I'm confused because the Third Octave Analysis VI has an output variable "octave spectrum" which is a cluster containing 2 arrays, one labeled 'center frequencies' and the other labeled 'band power'. Yet I don't think I convert to band power through that Vi.... or do I...? Or is this just a case of bad wording for the output array and I am infact getting the dB SPL and not dB power? I haven't been able to really figure out what everything does inside that Vi and all the documentation for that Vi seems to reference the EU units (which I'm assuming SHOULD be dB Pa rms, but I'm not positive).
Thanks for reading,
The more I'm looking at the octave analysis VI, the more I believe the measured value to be the SPL. It doesn't make sense for a recorded sound to be in power level since a power level is more tied to something with a known output power, such as a speaker. Additionally, the sound power should be in the units of Watts. I think this is just a case where I interpreted "band power" as units of dB Sound Power and not dB SPL.