I looked around for a post on this but couldn't find anything on the forum. Some of my audio files have a mirror image of the lower frequencies (below 12 kHz) at higher frequencies (above 12 kHz) - see screenshots attached. The audio is fine, I can identify the birds of interest from the audio clip. However, I imagine I can't use this data for any kind of spectral analysis.
Why do you think is happening?
I am seeing this for my AudioMoth recordings at some of my sites as well, @Pooja Choksi - did you find out any more information? Despite using the same configuration for all of my AudioMoths, I am only seeing these mirrored sonograms for some of them. Using RFCx Arbimon to visualize currently.
Before we speculate about the cause of this effect please post an original wav file of one of these recordings (ie EXACTLY as saved by the AudioMoth).
I haven't done the math on this, but I think this happens when audio files at sampling frequency X get padded to make them have sample frequency 2X. For example, if you try to turn a 22kHz recording into a 44kHz recording. See here for a discussion:
The recordings of "The Warbler Guide" suffer from this phenomenon as well.