Yes I have been using standard AA NiMH batteries fore my AudioMoth and they worked out fine. You probably want to take care that you pick a proper brand with reliable performance. I have been using the ones from Eneloop/Panasonic.

@Alex Rogers This brings up the question what would be a good lossy compression algorithm for noisy nature recordings. Obviously out-of-the-box mp3 with its emphasis on the human hearing range is a bad idea for, say, bat recordings. Instead you want to be able to tell the compression algorithm about the frequency range that you are interested in. Are there formats out there that would allow that kind of fine tuning?

@Edder Antunez I guess my recordings have too much white noise for lossless compression...

The AudioMoth produces .wav files, which is an uncompressed format. So you are correct that the level of noise and sounds does not change the file size. If you were using a compressed format like mpeg or mp3, then the file size could start to vary. As an aside: I recently tried a lossless compression algorithm (zip) on 2.48 GB of my night recordings and it only reduced to 1.99 GB, i.e. the compression rate was 0.8: not really worth it.

Thanks Robert for doing the work and reporting it. I'm intrigued about the difference in performance between the membranes. Are these full cases with only a small (membrane covered) hole for the microphone, or is the whole front of the case missing? Thanks Wim

Thanks Duncan. That's very interesting that they recommend a sample rate of 192kHz over a rate of 384kHz. My laptop's hard disk is very relieved to know that. Wim PS: There is no need to include the facebook id info in the link, just go to: https://somersetbat.group/advice/which-bat-detector/audiomoth/testing/ It's really unfortunate that the bat-ID community has decided to set up shop on facebook and not somewhere else less ephemeral.

Hi Tessa, I think my current bat settings work pretty good in my quiet neighborhood and they are: "sampleRate": 384000, "gain": 2, "passFiltersEnabled": true, "filterType": "high", "lowerFilter": 20000, "higherFilter": 65535, "amplitudeThresholdingEnabled": true, "amplitudeThreshold": 512 I'm still recording a fair amount of noise though, so I probably should increase my amplitudeThreshold and see if that helps. I try to ID my bat calls by hand so for my sanity it's best if I don't record those weak calls anyway. Wim

I haven't done the math on this, but I think this happens when audio files at sampling frequency X get padded to make them have sample frequency 2X. For example, if you try to turn a 22kHz recording into a 44kHz recording. See here for a discussion: https://taperssection.com/index.php?topic=171159.0 The recordings of "The Warbler Guide" suffer from this phenomenon as well. Wim

Hi Rob, What sampling frequency do you use for your recordings, and what settings do you use in Audacity to look at the spectrograms? Wim

That's surprising. Here in California I use a 20kHz high filter with 512 threshold and it does a pretty good job of not recording bat-less periods. I record in periods of 595 seconds with 5 second breaks so it's easy to throw away bad recordings. I always end up with a lot of data but fortunately that's because there were lots of bats. Wim

Did you accidentally turn on "amplitude threshold recording"? That would explain getting recordings of different lengths. See here: https://www.openacousticdevices.info/config-app-guide Wim

Maybe the 0s sleep trips things up? What happens if you program it with 5 seconds of sleep and a recording duration of 295 seconds? Wim van Dam

Thanks Alex. I just emailed Andy the following: Please find attached a photo of the crack that developed in my AudioMoth case. It wasn't there when I got the case and I have deployed it about a half dozen times. Looking at the photo it also shows how the case seems to be bulging on the side of the crack, suggesting that there is too much stress there. This bulging also shows when the case is empty, so it is not due to the AudioMoth being too thick. Thanks for your help with this. Wim

Same here. The clasp of my black case has a growing crack and will probably break completely if I keep using it. Maybe I can prevent the crack from growing with some preventive glueing and I'm curious what kind of glue people recommend for this.

Thanks Alex, it does indeed work for a 5cm diameter. I think that if the strap would have less hook (the rough part of Velcro), and more loop (the soft part), then it could accommodate a larger range of diameters. (Clearly we're talking minor details here; I'm really happy with it.)