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Wavelet versus Fourier analysis of Philautus spp. croaking [abstract]

L. Spithoven, M. Eens, N. Koedam and C. De Mol (2002). Wavelet versus Fourier analysis of Philautus spp. croaking [abstract]. Bioacoustics, Volume 13 (2): 206

 

Abstract: 

Male frogs produce acoustic signals that are used by females for recognition of conspecific mates. For communication to be efficient, mate recognition requires that there is a functional association between the signal (sender) and the response properties of the sensory system that decodes the signal (receiver). This correlation between signal and receiver can, by promoting assortative mating, restrict genetic exchange among populations and is therefore thought to constitute a crucial component in speciation. We recorded advertisement calls of Philautus spp. (Ranidae, Rhacophorinae) from the Western Ghats, India. In order to get as much information as possible out of the collected data, optimal analysing tools have to be developed. Frequency is generally considered to be one of the important species recognition cues. To analyse the frequency content (spectrum) and to observe changes in the sound spectrum (spectrogram), the traditional approach used in bioacoustics is based on Fourier analysis. A recent alternative to this classical tool is wavelet analysis, which has become quite popular in several disciplines both in theory and in practice. So far, however, it has been little used in bioacoustics. By computing wavelet transforms of the samples of the digitally recorded frog croaking, a more subtle analysis can be achieved and some chirps, which can hardly be detected through a Fourier analysis, are clearly revealed by wavelet techniques. Such wavelet-based analysis is expected to be of great help in identifying a set of most significant sound characteristic features or "signatures'' on which a more efficient population discrimination can be based. An understanding of the basis of such discrimination is expected to lead to a better insight into the evolution of the frog acoustic communication system.