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Audio Moth 20Khz Hum

Hi All,

I have a very annoying 20Khz hum on the Audio Moth, is this normal or is there a way to reduce or eliminate this? This image is the social chatter in a Common Pipistrelle roost, the 20Khz hum is right across the peak frequency of the bat chatter. NB: The Audio-Moth was operating in USB Live mode.

Many thanks

Andrew

5 comments

5 Comments

julie-annemurphy

Jul 07

Possible noise floor or grounding issue?

I can try to remove the hum in the audio for you if you post a copy?

Andrew Gilbertson

Jul 03

Hi Alex, thank you for your response. In the USB configuration covering the microphone with my finger virtually eliminates the hum at 18.9Khz. Moving the moth away from the laptop doesn't reduce this noise.

I've also configured the Audiomoth with the latest firmware 1.10.1 and put it out in the countryside well away from any manmade interference and you still get the interference. See attached file.

Many thanks

Andrew

Alex Rogers

Jul 03

Replying to

Hi Andrew, This looks like the normal sensitivity profile of the MEMS microphone. There is a little SD card write noise which is normally minimised by using SanDisk Extreme (red and gold) SD cards. The MEMS microphones are very sensitive to bat frequencies - much more so than small electret capsule microphones - but have a peak in sensitivity around 20kHz which appears as this banding in the spectrogram. Alex

andygilbertson

Jul 04

Replying to

Many thanks Alex

Alex Rogers

Jun 10

Can you describe the setup in more detail? It looks like normal ringing from the MEMS microphone. Can you share one of the WAV files? Sometimes laptops will generate additional noise. Could the source of the hum be your laptop? Does the hum decrease if you cover the microphone with your finger or move the AudioMoth away from the laptop?

Edited