Bat recordings: What are these weird patterns in my spectrograms?

[robmais]

Dear all,

 

I have been working on these bat echolocation calls for a while. Every now and then there is this weird drop in white noise followed by a peak at a wide range of frequencies. I hope there is anyone out there that has any idea what this can be. An example spectrogram of this weird pattern has been attached. The white noise is the sound between 60 and 70 kHz in this spectrogram.

 

Thanks for any help and suggestions,

Rob

[michel123456]

I have absolutely no idea since it is not my field at all.

But

If there is a drop, IMHO it must mean that what you describe as a white noise is not a white noise, it is a noise.

 

------------------------

There is a radio signal at 60 Khz for time & frequency standards.

http://www.armms.org/media/uploads/s_day_implementation_of_a_software_defined_radio_for_the_60khz_msf_time_signal.pdf

Edited March 30, 2014 by michel123456

[robmais]

Hi Michel123456,

 

Well that is a very good point, but makes it even more interesting. What is the sound than? I know they are not crickets or grasshoppers. Perhaps there is something wrong with my ultrasound recorder.

 

Thanks

I think I have found out what possibly is going on. I think it might be cyclic noise caused by either the device or electricity cables. Electricty cables here are all above ground, I'm working in Thailand. The pattern might be a drop of power in the electricity grid (which is really unstable here) or in the power of the battery of my device.

 

The following paper shows spectrograms with the exact same noise plus an explanation of what they are.

http://users.ece.utexas.edu/~bevans/papers/2013/PLCcyclic/cyclicPLCnoiseISPLC2013Draft.pdf