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You recorded bats. You are interested in social calls. Socials calls can be recorded by your microphone but they cannot be read by standard media player because...
- the standard media player are limited to certain frequencies
- your speakers cannot produce such high sounds
- your ears are not able to hear many of the frequencies emitted
- you formatted your records in a format that cannot hold very high frequency (for reason of optimizing data compression)
You might use some program like Adobe Audition in order to easily visualize the frequencies (vs time) of your record. (It might also help you finding all harmonics or performing Fourrier analysis)
This wiki article says :
This is a wide subject and there is still a lot to be discovered about bat social communication and how they use social calls in roosts and when flying. Generally a bat social call is not tonal, in other words it does not consist of a musical type note. Some bat detectors do not produce an accurate recording of a bat social call. Typically bat social calls use a lower frequency range than echolocation calls, and can thus be heard further away. Sometimes a bat will make a social call while echolocating which can cause confusion.
We can see and hear how the lower frequency social calls are heard at a greater distance than the higher echolocation calls as the bat approaches and departs. Zooming in on a spectrogram, social calls are atonal and repeated rapidly about five times in each call. The social calls are interleaved between the echolocation calls. They show a ragged frequency distribution around 20 kHz. Note the FD detector divides frequencies by 10.
The echolocation calls are single "hockey stick" calls at a higher repetition rate. At this scale the hockey stick shape is not very clear, but the end frequency can be measured as 45.2 kHz. A doppler shift is recorded as the bat approaches. The frequency was measured as it passes