Hi, I’m preparing the metadata to accompany my data and I have some queries related to my HydroMoth(s). I hope you can help me.
GAIN SPECIFICATION
I’m asked to introduce a specification of gain with one of the following two fields:
Gain_dB: Gain boost in decibels; or
Gain_rel: Uncalibrated gain boost such as a number on a dial.
Which one applies if I have configured my HydroMoth with Medium-High Gain. Is it 25 dB? And with medium Gain?
SENSOR
I have the HydroMoth devices ID (249C600363FB8D74; 249C600363EE19B7; 2453AC0263FB8CF0, etc), but I couldn’t find any information about the sensor used. Is it possible to know some of the following information?
Sensors: A record describing the sensors on the instrument. These fields describe the sensors used to collect data, they do not contain the data themselves:
SensorNumber: Index of a physical sensor that was used to collect the channel data.
SensorID: A value that uniquely identifies this sensor, such as a serial number.
ReferencePoint: Specification of the reference point used for this instrument.Sensor geometry measurements are relative to this point. When Geometry is specified in Sensor, Audio, or Depth, ReferencePoint is required.
Audio: A sensor designed for recording audio. Contains generic sensor fields above and:
TransducerId: Transducer identifier.
PreampId: Preamplifier identifier.
Many thanks for your help,
Lydia
Hi Lydia,
I would describe 'Gain rel' as '3'. That's the number that will appear in the GUANO metadata in the recordings and corresponds to 'Medium-High' gain. The actual 'Gain dB' is then 20 x log_10 (11 x 25) = 49 dB. The '25' value is the amplitude multiplier - a signal in at 10mV peak-to-peak comes out at 250mV peak-to-peak. The '11' is the default preamplifier amplitude multiplier before the software-controlled stage. With 'Medium' gain the 'Gain rel' is then 2 and the 'Gain dB' is 20 x log_10(11 x 15) = 44dB.
These numbers come from this application note - https://github.com/OpenAcousticDevices/Application-Notes/blob/master/Configuring_the_AudioMoth_USB_Microphone_from_the_Command_Line/Configuring_the_AudioMoth_USB_Microphone_from_the_Command_Line.pdf
Most of the other parts don't really make sense in the context of HydroMoth as there is no separate transducer and preamplifier - it's all contained in the same device and identified by the HydroMoth device ID. The actual sensor is a Knowles SPU0410LR5H-QB MEMS microphone but that isn't really what they are looking for here, as it's the design of waterproof case that will determine the sensitivity and frequency response rather than the actual sensor used: https://www.digikey.co.uk/en/products/detail/knowles/SPU0410LR5H-QB/2420974
I'd suggest you lobby whoever requires the metadata to change the format to allow other fields. For the sensor it should really just be 'HydroMoth' and the ID is the device ID.
Alex