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Scaling WAV files produced with NTI Audio’s XL2

 

Sometimes customers want to do more than simply listen to a WAV recording made by NTi Audio’s XL2.


For customers doing post-processing and analysis on recordings (e.g. MATLAB), the absolute scaling in engineering units (e.g. Pascals) is important. Unfortunately, the WAV format does inherently store data in engineering units, only percentage of full scale, 1.0 to -1.0.


Reading the Full Scale (FS) from the file name


By default, WAV recordings made by the XL2 include the Full Scale (FS) in the file name (e.g. 2019-10-17_SLM_012_Audio_FS129.9dB(PK)_00.wav)


Reading the Full Scale (FS) embedded in the file


The XL2 stores date and time of the recording within the wav-file (according to EBU TECH 3285 - Broadcast Wave Format BWF). This information is available through professional audio/video tools typically used in broadcast.


Here are some links to various tools for reading the data:


The scaling information is contained in the Description field. Here are examples:

Sound: 0dBFS = 109.7 dBSPL Time Zone: UTC-06:00 (DST)

Vibration: 0dBFS = 2.40 mps2 Time Zone: UTC-09:00 (DST)


Applying the full-scale value in MATLAB

For sound data, convert the full-scale value in dB (aka 0dBFS) and to a full-scale value in Pascal (Pa) using the formula


Pa = 20E-6*10^(0dBFS/20) (109.7 dBSPL converts to 6.11 Pa)


For vibration data, the full-scale value is already in engineering units; 2.40 m/s2 in the example data above.


Simply multiply the full-scale value by the unscaled in MATLAB. So a data point in MATLAB which was -.02315 would be -1.41 Pa.



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