hi CorBee, hi all!
very nice progress!
I have some comments on some of the posts made in the last days:
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sample rate: please note that in order to really accurately identify a large part of the bat species (Myotis for example), you really need a frequency response at least up to 125kHz, maybe even a little more. So my suggestion: use at least a sample rate of 250ksps ! Many bats use short calls of a few milliseconds that are frequency-modulated from way over 100kHz to as low as 20kHz. Many of the harder-to-identify species can only be accurately determined to species if you have good knowledge of the start frequency, end frequency, frequency of maximum energy, pulse duration and some more parameters. For that you need the entire call including the start, that may be above 120kHz. Thats why it is important to accurately record at least up to 120/130kHz.
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microphone response: the SPU0410 seems to work at least up to 100kHz, see my first ultrasound recordings:
https://github.com/WMXZ-EU/microSoundRecorder/wiki/Sample-recordings
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ICS43434: this is a digital MEMS mic, so you do not need a preamp, but the ICS43434 does not work for ultrasound, because the max sample rate is 51.6ksps, see here:
https://www.invensense.com/download-pdf/ics-43434-datasheet/
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OPamps & slew rate etc.: I read a little more on OPamps for amplification of audio and I found that the requirements for slew rate and gain bandwidth product are really uncritical, if you use a two-stage preamp (gain is distributed over two stages, for example 11 and 10, so total gain is 110 == 41dB) and your output signal is not too high (its +-0.6Volts peak for the Teensy ADC). However, it should be an ultra low noise type with noise density lower than about 10nV/sqrt(Hz) --> see here:
https://store.invensense.com/datasheets/invensense/Op-Amps-for-MEMS-Microphone-Preamp-Circuits7.pdf
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long unshielded wires: not sure about that: but in some of the uploaded photos you see long, unshielded wires for tiny audio signals very near to a microcontroller ;-). My suspicion is, that when using the shortest possible cable length and shielded wires, one can seriously decrease the digital noise that is being picked up by the detector, especially if you have a dynamic display for FFT etc (which produse lots of noise). But that is just my guessing
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Walter, I wonder how I can use a high enough sample rate (> 250ksps) with your microSoundRecorder that has a MULT of 1 (for reason of low noise). Do I have to change manually the function I2S_dividers? Or do the reasons for using MULT of 1 do not apply if I do not use the audio board, but the built-in Teensy ADC ?
All the best,
Frank