3.8
Calibration
Each SoundTrap is factory calibrated from new. The standard factory calibration consists of a piston
phone calibration at 250 Hz, performed for both low and high gain settings. The calibration data is
not shipped with the hydrophone, but instead made available online from the calibration page of
the Ocean Instruments website
http://www.oceaninstruments.co.nz/
The calibration data is provided as an end-to-end value. This measure is provided for both high and
low gain settings, and represents the SPL that will result in a normalised (±1.0) wav file with a
fullscale signal ie 2.0 units peak to peak.
Note that in contrast to traditional hydrophone systems, with SoundTraps there is no need to be
concerned with sensitivity in voltage terms. Because SoundTraps integrate the recorder and
hydrophone in a single package, there is a fixed relationship between sound pressure and the
resultant wav file data, thereby simplifying calibration and eliminating the need for voltage
calculations.
Application of the calibration data varies depending on the software used. Descriptions follow for
some of the most commonly used software.
MATLAB
To convert wav data to units of uPa, simply scale by the end-to-end calibration value. Example code:
[y, Fs] = wavread(filename) ;
cal = 173.3;
cal = power (10, cal / 20);
y = y * cal;
% read wav data from file
% value from calibration sheet
% convert calibration from dB into ratio
% multiply wav data by calibration to convert to units of uPa
PAMGUARD
PAMGAURD expects calibration data in terms of gain and ADC range. To work around this, specify a
preamplifier gain of the calibration value * -1.0 (eg -176.0) and specify the Peak-Peak voltage range
as 2.0 V.
