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The Acoustic Complexity Indices (ACIs): Theoretical and applied perspectives
  • Almo Farina
Almo Farina
Università degli Studi di Urbino Carlo Bo

Corresponding Author:[email protected]

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Abstract

The Acoustic Complexity Index (ACI) is one of the most used metrics in ecoacoustics, demonstrating reliability across a broad range of environments and ecological conditions. However, this index requires specific procedures to be applied in the correct way. Based on the “Canberra metric,” the ACI is an unsupervised metric formulated to extract information from fast Fourier transform (FFT) sonic matrices. The ACI measures contiguous differences in acoustic energy of each frequency bin i along temporal steps (ACItf) and of a temporal interval j along the frequency bins (ACIft). The aggregation of data after an FFT using a clumping procedure allows for better scaling of the sonic signals before the computation of the ACI. The application of a filter to reduce the effects of non-environmental signals produced by microphone electrical noise is mandatory to avoid masking effects. Due to a singularity of the index for values equal to 0, ACIs require ad hoc procedures to exclude from the comparisons pairs of elements of which one is equal to 0. The spectral sonic signature and temporal sonic signature are vectors obtained from the sequence of ACItf and ACIft values, respectively. The comparison between sonic signatures using the chord distance index returns spectral and temporal sonic dissimilarities that allow the evaluation of sonic patterns emerging at different temporal and spatial resolutions. The number of frequency bins, sonic variability, and sonic evenness are further derivative metrics that help to interpret sonic heterogeneity by distinguishing the temporal and spatial heterogeneity of sonoscapes. A change of the name of the “Acoustic Complexity Index” to the “Sonic Heterogeneity Index” is recommended.
12 Mar 2024Submitted to Oikos
20 Mar 2024Reviewer(s) Assigned
31 May 2024Review(s) Completed, Editorial Evaluation Pending
23 Jun 20241st Revision Received
26 Jun 2024Submission Checks Completed
26 Jun 2024Assigned to Editor
26 Jun 2024Review(s) Completed, Editorial Evaluation Pending
03 Jul 2024Reviewer(s) Assigned
16 Aug 2024Editorial Decision: Revise Major
28 Aug 20242nd Revision Received
29 Aug 2024Submission Checks Completed
29 Aug 2024Assigned to Editor
29 Aug 2024Review(s) Completed, Editorial Evaluation Pending
13 Sep 2024Editorial Decision: Revise Minor
14 Sep 20243rd Revision Received
16 Sep 2024Submission Checks Completed
16 Sep 2024Assigned to Editor
16 Sep 2024Review(s) Completed, Editorial Evaluation Pending
18 Sep 2024Editorial Decision: Accept