S&V Assistant - Getting wrong values?

[adalogue]

I have the 2013 version of Labview Signal Express Sound and Vibration Assistant (v7.0)

When recoring new or analyzing recorded data, I get very different values for sound pressure level depending which step tool I use.

1. Octave Analysis - total band power (slow, 1 sec time constant)

2. Sound Level - running Leq (1 sec)

3. Amplitude and Levels - (exponential), then formula for 20*log(p/p_ref)

These are underwater measurements, so reference pressure was set to 1 uPa during data acquisition and is displayed as 1uPa in amplitude axes. However, #1 values above are typically much lower (30 dB or so) than #2 and #3. I recorded a cal tone (145 dB re: 1 uPa) and it shows up correctly in the 250 Hz band from the Octave Analysis step, and a manual addition of all octave bands matches the "total band power". I don't believe the values report for #2 and #3.

Any ideas what may be wrong?

[Nathan-M]

How different are the values that you are seeing? 

The steps above all have various other parameters (averaging, filtering, etc.), so it is not entirely surprising that the values you are seeing are different. 

[BouvetSamuel]

Hello,

I have recorded a sound signal with S&V Assistant and set reference at 20uPa. But when i load the signal with an other computer reference have been change to 1 Pa.

So i have two questions, if is it feasible to change reference after loading ? Or an other possibility to fix that problem.

[Nathan-M]

How have you verified that your reference is changing when you load the signal on another computer?

Is the file that you are loading a TDMS file? 

The reference sets the 0 dB point of the scale. To change the reference, you would have to convert from db to Pa using the 20 uP as a reference, and then back to dB using whichever value for a reference you would like. 

Use the two equations to convert from your sound pressure level to dB.

All units in Pascal (Pa)

~p : pressure value given a dB value

p_0 : 0 dB reference

L_p : dB given a pressure value

[BouvetSamuel]

I have use prob on the input signals.

Yes i test the other types files too.

For the solution with equation the problem is VIs don't support the signal output of the fomula VI.