I recently purchased a batch of hydromoths and I'm curious if it's possible to calculate the sound pressure level. I'd like to ask everyone for the relevant data of the equipment.
Sensitivity1 S 94 dB SPL @ 1 kHz -38 dBV/Pa
Gain Medium
It seems I still need the ADC volts value to convert it into pascals for calculating the sound pressure level.
Has anyone figured it out or knows the ADC value?
Thank you, everyone.
Hi, The full conversion is that the microphone output is initially multiplied by 11 in a pre-amp. Then this signal goes into the software-controlled amplifier that, depending on the gain range (low or normal) and the gain setting, will apply another 0.33 to 30 times signal multiplication. The default is 15 and the values are shown in the table here - https://github.com/OpenAcousticDevices/Application-Notes/blob/master/Using_HydroMoth_to_Make_Underwater_Recordings/Using_HydroMoth_to_Make_Underwater_Recordings.pdf. The ADC then uses a differential input and a 2.5V reference for its conversion. This means that a signal with a peak-to-peak range of 2.5V will turn into a full-range 16-bit output from -32768 to 32767. This typically works well for the microphone in the air. Calibrating the HydroMoth is more tricky as you need to factor in the transmission through the case. This is also confounded by the presence of air inside the housing which makes the response dependent on direction and frequency. A calibrated underwater recording will typically be oil-filled to avoid these additional issues. Alex