short introduction for how to
proceed with evaluation of crane calls
How can you analyse crane calls (and other bord calls) if you are not willing to spend an additional several hundred Euros for the licenses of professional programs like „Raven Pro“,1 „Matlab“2 or „mathematica“3 (which I had used), each of which requires special subroutines. After a lot of research and frustrating attempts to find a cheap or even free solution, I ended up with two programs: One is „Audacity“.4 With this program, I can convert recordings from my smartphone into the more suitable *.wav format („File“/“export“/“export as WAV“), but above all, I can edit the files (remove disturbing background noises, amplify insufficiently audible calls – „Effect => Normalize“) or merge parts of different recordings.
On the other hand, I have the program „Avisoft SASLab Lite“5: It has gained a lot of functions in recent years. With this program, I proceed as follows: I open the wav file (either the original from my ZOOM recorder or a recording edited with Audacity), mark the call or the part of a call that interests me, and generate the „Power Spectrum“, the frequency spectrum with the steps „Analyze“/“One-dimensional Transformation“/“Power Spectrum logarithmic, Evaluation Window Hamming, Channel 1/Ok“. This gives a spectrum from zero to 22 500 Hz, completely unusable for my purposes in this form. So, I first put a grid over the result („Display“/“Grid“), a setting that remains for subsequent operations. Now, I click on „Display“/“Display Range“ and enter „X-Axis“ at Xmin = 0.6 kHz, at Xmax = 1.2 kHz in the window (this is the frequency range in which most grey cranes call)6; then, I click on „Edit“/“Smooth“ and enter „Average over 41 points“; the result is a graph with an unbelievable number of pages, which I first convert with „File“/“Print“ into a pdf of the same number of pages. Then, I print page 1 of this pdf file in horizontal orientation on paper, so that the DIN-A4 format is fully filled. Now, I can put the printouts of different recordings’ analyses on top of each other or hold them in front of a lamp: The „peaks and valleys“, if they are calls from the same pair, must be at about the same frequencies. Deviations of about five hertz are normal, as are differences in intensity (loudness) at each frequency; after all, cranes are not machines, but living creatures. The „mountains“ in the spectra show the frequencies with which a respective crane calls.7
1https://ravensoundsoftware.com/software/raven-pro/, developed and distributed by Cornell University (USA)
4For other bird species, of course, you first have to find out the frequency range in which they call, i.e., where their ground frequency range is (you do not need the overtones!). To find out, you create a spectrogram, which can also be used to identify annoying interjections that you can then delete with Audacity. Now that I no longer work with SoundForge, I create sonagrams online on the following website, unfortunately, without the free definition of the frequency range: https://academo.org/demos/spectrum-analyzer/
5For other bird species, of course, you first have to find out the frequency range in which they call, i.e., where their ground frequency range is (you do not need the overtones!). To find out, you create a spectrogram, which can also be used to identify annoying interjections that you can then delete with Audacity. Now that I no longer work with SoundForge, I create sonagrams online on the following website, unfortunately, without the free definition of the frequency range: https://academo.org/demos/spectrum-analyzer/
6For other bird species, of course, you first have to find out the frequency range in which they call, i.e., where their ground frequency range is (you do not need the overtones!). To find out, you create a spectrogram, which can also be used to identify annoying interjections that you can then delete with Audacity. Now that I no longer work with SoundForge, I create sonagrams online on the following website, unfortunately, without the free definition of the frequency range: https://academo.org/demos/spectrum-analyzer/
7Two examples of two different crane pairs: https://www.bernhard-wessling.com/power-spectrum-examples
