The need to standardize soundscape analysis metrics—A case study: Comparing temporal and spectral kurtoses of underwater sounds

Abstract

To evolve our ability to compare soundscapes across time, location and research groups, a standard suite of metrics is essential. Significant progress towards establishing standard approaches for quantifying the amplitude of the soundscape has been made in recent years, however advancing qualitative metrics has been challenging. Temporal kurtosis is often proposed as a soundscape metric that quantifies impulsiveness, and that filtering a sound for an animal’s audiogram could quantify the impulsiveness for animals with different hearing capabilities. This frequency-weighted kurtosis could be computed by filtering in the time domain, or perhaps by computing the spectral kurtosis over the hearing range. Comparing the two approaches provides a case study for the importance of standardizing analysis methods. Here the temporal and spectral kurtosis of common underwater sounds are compared. The band-limited temporal and spectral kurtoses are correlated for sounds from vessels, natural sounds, and seismic airgun surveys. They are substantially different for impact and vibratory pile- driving and the spectral kurtoses depend heavily on the analysis parameters, a result that is similar to a previous study of the acoustic complexity index. It is concluded that for qualitative soundscape metrics, standardized analysis methods are essential.