This page last updated April 26, 2004
There are a number of problems that we encounter when trying to analyze bat sounds. The first is the simple fact that we can't hear them, so we're stuck with having to use the computer. The second (and more important) is that it is very easy to get thousands of calls in just a few minutes of recording, which means you have a major analysis problem to deal with. To get around this, I'm using a system to analyze calls that the OSU batlab developed while I was there. This system automatically analyzes extracted bat recordings so that we can gather information on thousands of calls in a very short time. The third and final problem has to do with the presence of other sounds in the environment. As you can see in the image below, this extracted call is not a bat call (it's probably wind noise).
This was extracted because the extraction routine only looks at the amplitude of the signal, without paying attention to whether or not it's a bat call. We wrote a number of routines to eliminate those calls and keep them from being analyzed by mistake.
Sometimes problems crop up even when the sound actually came from a bat. In the figure below, you can see two overlapping bat echolocation calls.
In this case, we also wrote the analysis routines to ignore these calls, because the measurements would be incorrect, since it would be measuring multiple calls as a single one. This isn't something we had to do - as long as the calls don't overlap, it is possible to analyze them separately, so I'm hoping to get that working some time soon so that I don't have to throw out as many calls as I currently do.
When a call is judged acceptable by the program (and there are other reasons they can be excluded as well as the two reasons listed above) the program measures a number of time, frequency, and amplitude variables describing the call. It also fits a curve to the call shape to describe the shape of the call mathematically. The image below shows some of the measurements.
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