Hi, I have just downloaded the files from my Audiomoth which was set to record overnight. It produced 1600 plus files - most of which are noise - although I did pick up pipistrelle signals in some of them. The Audiomoth was housed in a case I downloaded from the internet and 3D printed (see attached photo). It incorporates an audio vent I bought from China. The weather was rainy. I attach one of the few traces (from kaleidoscope) that actually detected a pipistrelle (see 55 to 90 kHz) but the trace also shows a repetitive background signal at 10 to 20 kHz that is a feature of all files. Any clues what this signal is caused by and how I can avoid in future? Or is it a case of wading through all 1600 files to find the ones that contain bat signals? Should I adjust the amplitude threshold? I read on the forum that sound triggering is being developed presumably for this reason. Many thanks in advance .... (PS - this is the first time I have used an AM and I am new to this bat monitoring lark)
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Hi Richard, If you update the Config App here (https://www.openacousticdevices.info/applications) to the latest version you'll have all the options. All the firmware versions will work with all versions of the AudioMoth hardware. The filter is a first order Butterworth filter so the filter cut-off is not very sharp. Also bat calls tend to be quite loud and will often nearly saturate the microphone anyway, so you probably won't impact the low frequency bat calls too much. The key thing the filter does is remove all the very low <1kHz background noise which allows the threshold value to be set very low so you still trigger on quiet bat calls. Try 15kHz and let us know.
Hi Alex, My AMs are version 1.0.0. I have flashed them with the latest 1.6.0 firmware. However I don't get the option of "minimum trigger duration". Presumably this is because they are the older versions? Also I only have three tabs "Recording Settings", "Schedule" and "Advanced Settings" rather than the four that you have. Also won't setting a minimum frequency of 40kHz miss the calls of a number of UK bats that signal at around 20kHz (eg noctules, Leisler's Serotines and barbastelles). I think I will set the minimum to 15Hz in line with Simon's post.
Thanks @Alex Rogers for the handy explaination of some of these settings. I'm fairly new to the bat recording lark and I've been stumbling around in the dark a bit myself, so this is really useful.
I have managed to capture some bat calls (only really Common Pipistrelle, so far) - but once I've gotten the hang of the settings, I intend to make recordings away from the back garden.
I've been uploading my recordings to the BTO Acoustic Pipeline, for automated processing with some success - as hacking about with hours of recordings in Audacity is taking up way too much of my time.
The Acoustic Pipeline can identify 24 species of European bat, plus small mammals and some insects and can be found here