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We are currently analysing soil recordings using Acoustic Indices, and applying Acoustic Complexity Index to the 0-2 kHz range (there is no useful signal above this upper limit). The Acoustic Complexity Index (ACI) is as proposed in Pieretti, Farina & Morri (2011) A new methodology to infer the singing activity of an avian community: The Acoustic Complexity Index (ACI) Ecological Indicators 11(3)

Which other Indices could be usefully applied below the 2 kHz upper limit?

Is anyone aware of studies applying Indices in narrow frequency ranges like this?

Thanks

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  • $\begingroup$ Could you include a reference to the 'acoustic indices' and 'acoustic complexity index' that you're referring to? It might be helpful if you explained a bit more about your research questions so community members might be able to give you other suggestions. $\endgroup$
    – ASimonis
    Commented Jul 6, 2022 at 0:18
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    $\begingroup$ Thanks. The Acoustic Complexity Index (ACI) is as proposed in Pieretti, Farina & Morri (2011) A new methodology to infer the singing activity of an avian community: The Acoustic Complexity Index (ACI) Ecological Indicators 11(3) $\endgroup$
    – Carlos Abrahams
    Commented Jul 6, 2022 at 6:36

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In the noise monitoring world, we regularly look at Third-octave Levels (TOLs) to describe the soundscape, especially in the lower frequencies you are interested in. We use them to help describe increases in anthropogenic pressure

The linked article can be found in:

Meggitt, J. A. R. (2017). On in-situ methodologies for the characterisation and simulation of vibro-acoustic assemblies. University of Salford (United Kingdom).

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I suppose you can calculate any acoustic index just on the smaller bin - ie get seewave to calculate for example ACI in the limited range.

Or downsample to 4 or 8 khz and then run your normal scripts in R.

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    $\begingroup$ Please avoid using unexplained abbreviations. Not all users will know what ACI is. $\endgroup$
    – etgriffiths
    Commented Jul 6, 2022 at 6:07
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    $\begingroup$ Thanks Simon. My thought/concern is that by reducing the analysis bandwidth of the Acoustic Complexity Index, I am also reducing the number of frequency bins used in the index (to only two?), and thereby reducing the power of the index?? $\endgroup$
    – Carlos Abrahams
    Commented Jul 6, 2022 at 6:39
  • $\begingroup$ We have to ask Jerome Sueur. I think the number of frequency bins are preserved. Definitely if you downsample ahead of time they should be preserved. $\endgroup$
    – Simon Linke
    Commented Jul 7, 2022 at 0:11
  • $\begingroup$ Number of bins won't be preserved unless you downsample, or you change the window length to match the equivalent spectrogram resolution found in the original recording. $\endgroup$
    – EcologyTom
    Commented Jul 7, 2022 at 8:13
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You might check out the methods used in these papers -

Non-native species change the tune of tundra soils: Novel access to soundscapes of the Arctic earthworm invasion.

Sounding Soil: An Acoustic, Ecological & Artistic Investigation of Soil Life

And as alluded to in previous comments, you could also just run a bandpass filter and calculate the indices on the filtered recordings.

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