The amplitude, or intensity, of the calls can be seen in the sonogram since it is represented by the intensity of the colour. What is of interest is the peak frequency, which can easily be analysed using Audacity. Here's a Common Pipistrelle from one of my recordings, and the peak frequency:
The recordings are full spectrum, and using the Wolfson Audio Card are at the maximum 192kHz sample rate. This allows analysis up to 96kHz which is good enough for most UK bats (Lesser horseshoe is around 110kHz).
Audacity shows the actual recorded frequency, since it is full spectrum. The "low frequency" call that I think you are referring to are social calls, which are louder are are usually at a lower relative frequency in comparison with echolocation calls.
I power the Pi from a "Power Bank": https://www.modmypi.com/raspberry-pi-ac ... power-bank
Hope these answer your questions. A question for you: where is your local bat group?
Let me know how you get on if you use your Pi to record bats.
keviom wrote:Hy Hystrix,
I have just come across your article and found it interesting as I am currently looking for a recording / analysis equipment to add to my heterodyne detector and move on to the next level of species identification.
I have just a some questions which I am hoping you might be able to answer.
Were you able to see and analyse the amplitude of the recorded calls?
Is this is a frequency division , time expansion or full spectrum type recording?
Is there a multiplying factor for the calls, or did audacity show them at the frequency they were actually sending at (the Pipistrelle calls, August 2014 seem quite low frequency which is why I ask)
Finally, how do you power the Pi and the microphone when out and about please (I'm a newbie to the Pi world)
Sorry to ask so many questions, but if this works like I'm hoping it could become very useful in our local bat group.
Thanks in advance