VT USA-168A/B Real Time Underwater Sound Analyzer Manual Rev. 1.5
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Adjustment of Input Digital Gain
Only when MME driver is used, the input digital gain can be adjusted by clicking the
respective radio buttons beside the “Line In 100%”, “Line In 80%”, “Line In 60%”, “Line In
40%” and “Line In 20%” in the above figures. It should be generally kept at “Line In 100%”.
These input digital gain settings have no impact when ASIO driver is used.
1.5.2 Adjustment of Input Gain via Hardware Gain Knob
You can adjust the input gain by turning the gain knob on the XLR-to-USB sound card (see
figure above). To account for this gain adjustment, you will have to update the “Probe”
switch position (see figure below) accordingly in Multi-Instrument’s toolbar.
If the “CLIP SIG” LED lights up red, reduce the gain.
1.5.3 0dB Reference Vr
The “0dB Reference Vr” in the Calibration Setting dialog box is used to finally calibrate the
input voltage to dBSPL. The input voltage here should be considered as a relative value as
the actual input is not a voltage but a sound pressure. The “0dB Reference Vr” is the
parameter to be recalibrated if a sound level recalibration is necessary. To do the
recalibration, simply enter the actual sound level value into the “Actual Value” edit box and
the measured sound level value into the “Read Value” edit box, and then press the
“Calculate” button once. It should be noted that the Sensor Sensitivity is kept at 1V/V in his
method.
In case you want to display the measured raw data in Pa rather than Volt, then you should
enter the “actual” Sensor Sensitivity in V/Pa, which can be calculated using the following
formula:
Sensitivity = [“0dB Reference Vr” (in Volt)] / [Standard 0dB Reference (in Pa)]
