Using frequency ratios to study vocal communication

Most research on animal vocal communication analyses frequency measurements on a linear scale, but the mechanisms of pitch perception and of certain aspects of vocal production are better described on a logarithmic scale, that is, as frequency ratios. Thus, for the majority of questions in vocal communication it is advisable to use log-transformed frequency, and the objective of this article is to encourage researchers to adopt this procedure. To illustrate this transition in methodology, I present two reanalyses of work on vocal communication, at the within- and among-species levels. Changing from linear to logarithmic scales yielded qualitatively identical conclusions, even in the among-species example where larger differences in absolute frequency can weaken the correlation between measurements at these two scales. These results suggest that conclusions of past work should generally be robust, at least when the absolute frequencies being compared do not diverge excessively. Results became stronger in the among-species example, suggesting that, as expected, frequency logarithms improve the ability to demonstrate biological phenomena. I hope that this discussion will motivate researchers to analyse frequency on a logarithmic scale for most research goals on vocal communication.