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I am working on conducting an a playback experiment with PODs and I am running into a few difficulties. The hardware set up for the playbacks is similar to that in Amundin et al., 2022/ Nuuttila et al., 2018.

As part of the plan I have .wav files of harbour porpoise vocalizations that I wish to play in a range of playbacks. I set up a configuration in PAMGuard to play the files with the National Instruments device as the sound output, which appears to compute but during some testing it seems the PODs aren’t picking anything up.... My thoughts on this are that perhaps it’s because the recordings are short sequences of clicks/buzzes, but aren’t ‘click train like’ enough to be recognised by the PODs? So compiling a longer sequence may be an option there? Or maybe I’m missing something else?

Also, just to note, I was getting an Error for a while in the Java code of PAMGGuard: "NiDaq Error PlaybackData code- 2000561. Attempted writing analog data that is too large or too small. Change Minimum and Maximum value to reflect the range of the Channel." However I figured that may have been an issue with specified voltages, and it hasn't occurred when playing the files over the last few days.

Additionally, I wanted to explore the use of artificial click sequences as I have seen this done a few times in the literature. It is my understanding that these sequences are generated sine waves, where you can specify the interval, frequency, source level etc. I have attempted to use the Labview software to play the .wav files and generate a ‘porpoise like’ waveform for analog output to the National instruments device and transducer but my technical skills here are limited (that’s why I was leaning towards the PAMGuard option but it hasn’t been working in my favour…). I thought I would ask if anyone could point me in the direction of a working Labview configuration for this purpose (analog output of .wav/generated signals), or have any advice on how to construct one? Labview VI's I have previously tried have required some subVI's that I could not locate, or have had bug issues when sending the signal to analog output.

Any help or advice is appreciated.

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2 Answers 2

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You have to carry out two tests:

  • is your transmitter working
  • is the POD working

Consequently, you should in addition to the POD record the transmitted signal with a standard hydrophone and compare recordings with the transmitted signal. If that part is working, you can address the POD settings.

Testing transmission with a standard hydrophone would also apply to synthetic signals.

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  • $\begingroup$ Thank you for your advice. It is part of our plan to test the playback with another hydrophone. Which if nothing else it can help identify where the issues with the set-up lie. $\endgroup$
    – NicT
    Commented Feb 21, 2023 at 13:42
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This seems to be a perfectly sensible way to use PAMGuard and we certainly use the same set up. One thing to be careful of is that the output sample rate (in the sound output module settings) is still set to the frequency of the recording you're playing back. Recent versions may automatically set the output rate at 48kHz and decimate the data down, which would obviously wreck the signal. If you can, bench test the output with an oscilloscope before going into the field.

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