Sound triggering

Thank you for the sound trigger system. In general it seems to work quite nicely on completely calm nights with high filter set at 15kHz and 196, 250 and 384 samplings a good balance is found at a amplitude level of ~120-130. At low amplitudes below 80 intrumental effects create false alarms and trigger is not effective any more. I am quite satisfied, thanks for the wole team!

Hi,

Yes I agree, it would be so awesome to have a form of sound triggering function. I only joined here now so if it's already released and announced, please kindly point me in the right post direction.

Thanks so much.

Hi, any info on a pre-buffer for use with bats would be appreciated?

I have been looking at spectrograms [will call these spectra for short] from 4 Audiomoths mainly at 384kHz but also lower sampling rates of 48 and 96kHz. The audiomoths have been physically far from each. I have placed them in vertical and horisontal positions. Furthermore the locations are such that no other source of electricity is not within 500m and most often not within 4km. At low sampling rates the spectra are quite clean, and make nice recordings. The sensitivity of the instrument at high frequenscies is good.

At high sampling rates there are some problems. The good thing is that most of the instrument based issues show as vertical or horisontal bands (or their mix) only. I have not noted interference signals with siginificant "tilted" what you expected from most (European) bat calls, so in principle they are separable. However, the horisontal, internal (and external) electric like signals in the spectrum can mimic horseshoe bats and similar sounds. The most consistent non-thermal instrument noise at 384kHz is a wide spectrum buzz repeating at a rate of about 25 times/sec (which is close to the rate in a grasshopper warbler song!). This signal is mostly quite weak at audible frequencies at 384kHz sampling, but in one audiomoth it is clear all the way to ~0kHz. The same signal is present at 96KHz sampling but at at rate of about 6/sec, and appers significantly weaker. In time steps the interval of the buzzes seems to be 2^14 points = 16384 (the size of the write block?) independent of sampling. The reduction or abolition of this noise signal would clean up the spectrum significantly, and make noise triggering truly feasible.

Another noise type present in all recordings and all my devices is a strong horizontal tone at ~20kHz which lasts about the same time as the previous signal, but shows many quite strong harmonics. This or its harmonics would cause most likely an extra trigger. Fortunately it occurs long intervals 2 to 22 seconds. The timing and the exact frequency varies a bit. The signal can recall a noctule bat in priciple. This sound appears to be repeted occasionally but normally followed by a loud "2^14 point type " session for a varying length of time and even up to 15 seconds.

Sound triggering is going to be essential if these are going to be of any real use for bat surveys. I'm interested in the response to Barry's question above.

Sound triggering will be key for our bat work where it is important to record for at least 5 days but not have masses of files of background noise. Suspect having it would vastly increase interest in this kit as a research tool

Will it be necessary for prebuffering, If the presence or absence of a bat is all that is required then prebuffering would not be essential enough of the call could be recorded to identify a species after triggering, and being able to record for a preset interval after triggering would also be of use.

Could this be done with an unmodified AudioMoth by changing the firmware.

Barry

Also received my units and got them working but have only recorded 5000 files of the waves so far! I had a Peersonic unit out for bats that only recorded 2 files so would love to have sound triggering to extend card use, battery life and time to review files. Thanks

Alastair

Having just received my units and detecting a Pipistrelle on it’s first trial use I would like to reinforce the need for an effective sound triggering system.

Martin

Hi Harry,

We are still in the process of restructuring the sound triggering functionality for the current AudioMoth hardware. It is possible to monitor and record specific frequencies with AudioMoth and we have deployed this in the past in Cuba. We use an external SRAM chip as the prebuffer and analyse data in this buffer before recording it to the SD card.

We will send an email to all subscribers when the initial triggering code is released.

Thanks,

Andy