Unfortunately, the time-expanded version of the same recording is in fact a recording of free-tailed bats near a cave, so there is no original to compare it to. Still, we can more or less safely assume the original is a steep FM signal with a QCF tail. What we see in the compressed recording is that the FM sweep doesn't come through very well. The QCF part is at 60 kHz, so we expect a second harmonic at 120 kHz, which we find instead at 180 kHz, or is the sound in between the second harmonic? Low amplitude calls have a tendency to drop in frequency, down to very low frequencies, which is obviously undesirable. It could well be that the sound file was just to give an impression of the sound quality, so we are looking forward to seeing more recordings with the future detector.