Field-testing the Prototype Device

An earlier post described my initial steps in building an audio monitoring device, and over the last couple of weeks, I have worked on putting the electronics inside an enclosure that is both waterproof and will not be too obtrusive when installed in a tree. We refer to it as the “bird-box”. The box is made largely of 3mm plywood, with some thicker wood framing. It’s been stained and varnished to weatherproof it. The design enables easy separate access to change the battery without dislodging the Raspberry Pi Zero W processor and the Ultramic. On the inside, we use hermetically sealed plastic lunch boxes to hold the sensitive electronics, with sealed punch-throughs for the various connecting cables. It’s cheap and very effective.

Our next step was to carry out some field-testing of the device. We decided to do this in the private garden of a University of Edinburgh property, close enough to the Meadows to capture representative samples of sounds in the environment. I installed a temporary WiFi access point in the building to pick up the data from the prototype device in the garden, which is collected on a laptop also sited within the building.

The recording device placed outside for 72 hours in the garden

Here’s a small sample of what we recorded over the three days of wind, snow, rain and freezing temperatures. The unit performed well in these challenging conditions, including the 30,000 mAh power bank.

This audio sample is indicative of what kinds of things we can detect in the urban environment: an emergency siren in the background, a stonemason working on a nearby building, and a snatch of bird song. The spectrogram below illustrates the different frequency ranges at which the sounds occur, from 0kHz up to 20kHz.

  • The bottom pink line is ambient sound.
  • The faint wavey pink line above that is the siren.
  • The strong pink fence-like pattern above that is the sound of the stonemason tapping away.
  • Finally, the little pink burst (between 3kHz and 5kHz) just before the last two taps from the stonemason is the clearly-audible bird song.

Listen again whilst looking at the image and you can observe how the sounds interact with each other.

We are excited to see that the recording device, the WiFi router and the computer all seem to be working together well.