This function computes the Normalized Difference Soundscape
Index as described by Kasten et al. (2012).
Usage
NDSI(x, anthropophony = 1, biophony = 2:8, max = FALSE)
Value
A numeric vector of length 1 giving the NDSI value.
Arguments
x
a two-column numeric matrix computed with soundscapespec.
anthropophony
a numeric vector defining the frequency band(s) of
the anthropophony (in kHz).
biophony
a numeric vector defining the frequency band(s) of the
biophony (in kHz).
max
a logical, if TRUE then defines the biophony as the
maximum - not the sum - of the 2 and 8 kHz frequency bands
Author
Jerome Sueur
Details
NDSI aims at estimating the level of anthropogenic disturbance on the soundscape by
computing the ratio of human-generated (anthropophony) to biological
(biophony) acoustic components found in field collected sound
samples. In terms of frequency, the anthropophony is defined as the [1-2[
kHz frequency bin and the biophony as the [2-8[ kHz frequency bins of a
soundscape frequency spectrum (see soundscapespec).
NDSI is computed according to:
$$NDSI = \frac{(biophony - anthropophony)}{(biophony + anthropophony)}$$
NDSI varies between -1 and +1, where +1 indicates a signal containing
no anthropophony.
References
Kasten, E.P., Gage, S.H., Fox, J. & Joo, W. (2012). The remote
environmental assessment laboratory's acoustic library: an archive for
studying soundscape ecology. Ecological Informatics, 12, 50-67.