Surrey
Bat Group
Bat Sound Analysis
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Surrey
Bat Group |
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Bat detectors have been used widely by members of bat groups and others for making the ultrasonic calls of bats audible. A number of different technologies are available for processing the sounds which bats produce, but until recently it was only the very expensive time expansion detectors which were able to produce a suitable output for computer analysis. However Stag Electronics have recently brought out their new Duet detector which makes use of both stereo channels, sending a heterodyne signal to one channel and a frequency division signal to the other. The heterodyne output is the only one to be played back through the loudspeaker, as that is of most use for identifying bats in the field, while the frequency division output is only available through the detector's recording port. The advantage of this method is that frequency division calls can be recorded onto suitable media, such as a minidisc, and played back through the soundcard of a PC for detailed anlysis. There are specialist programs for performing this analysis, but they are quite expensive. However other sound analysis programs such as Cool Edit, Gram and Soundruler can readily be downloaded, at least as evaluation copies, over the internet. Setting up your computer and minidisc to do this should be straightforward, but in practice there are a number of pitfalls which have prevented many of us from succeeding in this area. Following a number of training sessions which Dr Colin Catto of the Bat Conservation Trust's National Bat Monitoring Programme has given to the Surrey Bat Group we have put together this simple guide to using Cool Edit. If you would like to hear what a bat call sounds like, or if you would like to download some .wav files to analyse yourself, we have provided a few small sample files below. Most of the reference calls available to download on the web are time expanded, but we hope to expand this collection as a resource for those interested in comparing calls recorded using frequency division alone. 45 and 55kHz pipistrelle .wav file size 62k 55kHz pipistrelle social calls .wav file size 81k Daubenton's bat .wav file size 73k Serotine .wav file size 199k Noctule .wav file size 173k Nathusius's pipistrelle .wav file size 199k recorded over the river Mole at Esher in August 2002. Brown long eared .wav file size 298k recorded emerging from a roost in July 2003. |