Hello!
In our research, we are using a Zoom H4n Pro portable recorder for underwater sound recording. We need to take absolute measurements of the sound pressure level and for that we need to know the characteristics of the recording system (like the sensitivity of the transducer and how much gain is added). However, we are struggling with the "rec level" scale of the recorder (that goes from 0 to 100), and how it translates to gain in decibels.
My questions are:
- How to know exactly how much dB gain was set in the input "rec level"?
- at which rec level equals 0 gain and 0 attenuation, would it be at 50 (the intermediate level)?
Thanks for the help,
Isabel
Dear Isabel,
Never use dB scales if you do don't master the art of using logarithms! Make a refresh!!!
If the recorder is properly calibrated, 1 is 0dB, 10 is +20dB and 100 is +40dB gain (dB is 20 log decimal of...). 50 turns as 20*log50 in dB. 0 gain and 0 attenuation means gain=1 and/or attenuation=1 which is 0dB - that's totally basic!
In any case to be sure you can record a calibrated periodic signal from a basic lab signal generator (e.g. 10mV) and assess the gain after recording...
I will add that the sound level reference is not the same underwater than for airborne sound, so the absolute dB scale has to be reverted into Pa. While the 0dB = 2.E-5 Pa is unanimously acknowledged as reference for airborne sound (based on the agreed audition threshold of humans), there is a variety of 0dB references underwater! The most common is 0dB=1micro Pa
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