Experimental setup.

<p>The microphone array with 48 channels was connected to the recorder and a Laptop, and placed around 8 meters from the focal elephant.</p

Sound visualization of African elephant rumbling vocalizations.

<p>Examples of nasal and oral rumbling vocalizations from three female elephants, Messina, Nuanedi and Shan. Figures A, C and E give examples of nasal rumbles, B, D and F give examples of oral rumbles.</p

Spectral characteristics of nasal and oral rumbles.

<p>Spectrograms and power spectra showing an example of a nasal (A, B) and an oral (C, D) rumble, indicating formant positions (both rumbles uttered by Nuanedi, 10-year-old female).</p

Results of the acoustic analysis.

<p>The age and the sex of each recorded individual, the number of orally and nasally emitted rumbles (and the percentage of those recorded in each context, respectively), and the mean duration, mean fundamental frequency, mean formant frequency values 1 and 2, and mean sound pressure level (SPL) ± SD of rumbles per individual are presented. The estimated vocal tract length (VTL) for each individual based on the spacing in Hz between formants 1 and 2 for nasal and oral rumbles is also given.</p

Automatic classification of rumbling vocalizations.

<p>Numerical descriptors (averaged LPC spectrum) for all sound samples in the experiments. Each column of the matrix represents one descriptor of a rumble. Red represents spectral peaks while blue represents low spectral components. The descriptors of the nasal and oral rumbles show significantly different characteristics.</p