DD4WH
Well-known member
Hi CorBee,
your progress is really fantastic! Unfortunately I do not have the time to really test all your improvements . . .
Just a few comments from my experience:
* I would use a max sample rate of 281kHz (not higher), then you have a freq response up to about 140kHz. Thats enough for almost all bat analysis purposes and -more important- I doubt that your cheap mic picks up freqs above 140k
* from that perspective, I am a little sceptical about your spectrogram showing three harmonics of P. pipistrellus. I think that at least the last harmonic (F end = 135k) is a pure artefact. I have never seen higher harmonics having higher energy (than lower harmonics) in P. pipistrellus (an exception are the Rhinolophus bats, where the second harmonic has the highest energy, even higher than the first). I have seen similar artefacts in my recordings in those cases where the ADC was at the overloading point and the distortion of the waveform was overemphazising the harmonics (because the waveform approaches a square ;-)), so I would like to see more spectrograms of your system with lower amplitude (to be sure that the ADC is not overloading): in those cases, I would predict that the harmonics would be much weaker and there would be no harmonics above 140k, maybe analog gain in the codec is a little too high
Frank
your progress is really fantastic! Unfortunately I do not have the time to really test all your improvements . . .
Just a few comments from my experience:
* I would use a max sample rate of 281kHz (not higher), then you have a freq response up to about 140kHz. Thats enough for almost all bat analysis purposes and -more important- I doubt that your cheap mic picks up freqs above 140k
* from that perspective, I am a little sceptical about your spectrogram showing three harmonics of P. pipistrellus. I think that at least the last harmonic (F end = 135k) is a pure artefact. I have never seen higher harmonics having higher energy (than lower harmonics) in P. pipistrellus (an exception are the Rhinolophus bats, where the second harmonic has the highest energy, even higher than the first). I have seen similar artefacts in my recordings in those cases where the ADC was at the overloading point and the distortion of the waveform was overemphazising the harmonics (because the waveform approaches a square ;-)), so I would like to see more spectrograms of your system with lower amplitude (to be sure that the ADC is not overloading): in those cases, I would predict that the harmonics would be much weaker and there would be no harmonics above 140k, maybe analog gain in the codec is a little too high
Frank