How Index Selection, Compression and Recording Schedule Impact the
description of Ecological Soundscapes.
Abstract
1. Environmental soundscapes are increasingly being used as descriptors
of ecosystem health and vocal animal biodiversity. Soundscape data can
quickly become very expensive and difficult to manage, so data
compression or temporal down-sampling are sometimes employed to reduce
data storage and transmission costs. These parameters vary widely
between experiments, with the consequences of this variation remaining
mostly unknown. 2. We analyse field recordings from North-Eastern Borneo
across a gradient of historical land-use. We quantify the impact of
experimental parameters (mp3 compression, recording length and temporal
subsetting) on soundscape descriptors (Analytical Indices and a
convolutional neural net derived AudioSet Fingerprint). Both descriptor
types were tested for their robustness to parameter alteration and their
usability in a landscape classification task. 3. We find that
compression and frame size both drive considerable variation in
calculated index values. However, we find that the effects of this
varaiation and temporal subsetting on the performance of classification
models is minor: performance is much more strongly determined by
acoustic index choice, with Audioset fingerprinting offering substantial
(12-16%) increases in all of classifier accuracy, precision and recall.
4. We advise using the AudioSet Fingerprint in soundscape analysis,
demonstrating its superior and consistent performance even on small
pools of data. If data storage is a bottleneck to a study, we recommend
Variable Bit Rate encoded compression (quality=0, 23% file size) to
reduce file size without affecting most Analytical Index values. The
AudioSet Fingerprint can be confidently compressed further to a Constant
Bit Rate encoding of 64kb/s (8% file size) without any detectable
effect. These recommendations balance the efficient use of restricted
data storage against the comparability of results between different
studies.