Overview
Terra makes use of the BirdNET 6K model, a global Bird ID model developed by Cornell University, identify bird sounds. Here's the basic process:
1. The Terra samples a small segment of audio from both microphones
2. The Terra then analyzes the audio using the BirdNET 6K AI model, however, other models will be available in the future
3. If one or more birds are detected, the sound is converted to a FLAC audio file and uploaded to our servers with the associated meta data, such as species, confidence, and the date and time
4. The bird identification is provided to your mobile app or Featherworks website
About Detecting Sounds
Range
It would be nice if we could give an exact distance or sound level that Terra Station can identify birds from, but that's not easily done since there are a number of factors involved. As a general rule, Terra can hear everything that a person with very good hearing can, plus a little bit more. So if you can hear a faint bird sound standing next to Terra, then Terra can hear it as well. Sound travels with different amounts of efficiency depending on things like temperature, humidity, wind direction and speed, and objects between the sound and the hearer. So you may find that a sound is easier to detect one day and harder the next.
Optimizing Detections
There are a few things you can do to optimize your bird detections with Terra. Remember that there are two factors in getting a good sound for identification: 1. the volume of the sound of the bird 2. the volume of the other sounds around it. In audio recording people refer to the signal-to-noise ratio, which is sometimes used to describe the ability of a microphone to detect a sound without introducing its own, self-made noise (like the hiss you get when you turn up a speaker). It can also be useful to think of the signal-to-noise ratio as the bird sound vs the background sound. For example, if I have a bird making a barely audible "cheep", but the background is silent, then Terra will likely be able to identify it. But if that sound is surrounded by road noise, then the road noise can drown out the cheep and it won't be picked out by the Terra. This can be true even for loud sounds when the background noise is high enough. So overall we want to get as close to bird sounds as possible, but simultaneously avoid any loud background sounds.
That might mean that instead of placing your Terra right under the bird feeder in your front yard, which might pick up a lot of road noise, you might get better sound by placing it around the side of the house, where it can still hear the birds but where the road noise will be largely blocked.
This is also why it's not necessarily the case that placing the device high up will give you the best listening experience. It is true that it may be able to pick up migration sounds and radio tags a bit more easily, but placing the microphone high will also pick up road noise and other sounds well, too. So the benefits may not outweigh the drawbacks ... the additional background sounds could obscure some of the bird sounds, and it also might not be as pleasant a listening experience.
Placing your Terra lower to the ground and close to cover, feeders or a water source will often pick up more birds on the ground, and still pick up migration sounds. It will also help to block extraneous noise like traffic, which is (unfortunately) nearly ubiquitous in most areas where people live. In fact, you might find that putting your Terra on the other side of the house from the road, or behind a small hill or even a mound of dirt can help block those kinds of sounds, and give you more wildlife sounds instead.