It’s usually pretty easy to spot sounds above 500Hz in spectrogram analysis software, but many important bioacoustics happen way below that frequency and can often be overlooked. In this tip from the team, we’ll show you how to visualise low frequency sounds in AudioMoth Play, our online tool that lets you view, listen to, and analyse your AudioMoth recordings. You can use this tool to view WAV files, experiment with filters, tweak the configurations and export them for use in the AudioMoth Configuration App and then apply them to the AudioMoth hardware. 

Here is a video made from AudioMoth Play of an elephant rumble. It has been played back twice as fast so you can hear the infrasonic rumble. It is displayed at the 8kHz sample rate it was recorded at. You can just about make out the elephant rumble at the bottom of the spectrogram. 

To see the low-frequency bits of the rumble in AudioMoth Play, just click on the settings cog.

Enable ‘Low Frequency View’ and click Apply. 

Once you’ve done that, you’ll see a new ‘Low Frequency View’ tab appear. Click on it, and you’ll be able to visualise the low frequency spectrogram of your recording straight away. 

It is quite fascinating to see what is tucked away at these lower frequencies. Here is a video made from AudioMoth Play, where the same elephant rumble is played back twice as fast and at the new 500Hz sample rate. The rumble is now clearly visible. 

Bonus hints: 

1. If you want to record sounds below 48Hz on AudioMoth, make sure you ‘Disable the 48Hz DC blocking filter’ in the AudioMoth Configuration App before deploying a device.

   
   

   

   
   

2. To improve the visualisation of quiet sounds like this one, you can use the ‘Use dynamic spectrogram colouring’ to enhance the colour of background sounds.
   

   

   
   

   Here is an image made from AudioMoth Play, showing the same elephant rumble with dynamic spectrogram colouring. It has also been zoomed in on the amplitude plot.