There are characteristics of sounds found in nature which differ from sounds produced by humans. Marine animals have adapted to natural sounds over the eons. We know that some of the sounds produced by humans are compromising natural acoustical relationships. So focusing on the differences between natural and un-natural sounds can give us a handle on how to express potential impacts to marine acoustic habitats.
One characteristic we are exploring is “kurtosis” which is a numerical expression of how “rough” or screechy a sound is. If you take two sounds at equal amplitude, and approximately equal frequencies – such as a bowed violin string and fingernails skittering across a blackboard, it is clear that one is sweet, and the other agonizing. “Kurtosis” expresses this quality difference in a numeric form.
Kurtosis is a statistical expression of signal variability over time. There is no constraint in the time domain, so the metric can be used across all frequencies – from high frequency communication sonars to thumping of marine pile driving. We believe that we will find a correlation between kurtosis and acoustical compromise.