Contribution
Analyzing Polyphonic Vocal Patterns of Ross Seals
* Presenting author
Abstract:
This study analyzes aerial recordings of Ross seal (Ommatophoca rossii) vocalizations, revealing their unique polyphonic structures, consisting of a low-frequency harmonic complex tone (LFHCT) and an inharmonic complex tone (ICT). The LFHCT maintains a very steady pitch, while the ICT shows a characteristic frequency sweep. A generator model was developed, synthesizing these vocalizations using a first oscillator that produces the LFHCT, which drives a second oscillator that produces an amplitude modulated sweeping harmonic complex tone. In this way, the inharmonic components of the ICT can be traced back to distortion products (combination tones) between the LFHCT and the harmonic high-frequency sweep. The generator model can be perfectly tuned to the recordings, and the clean Ross seal vocalization can be extracted from a noisy recording using a matched filter. Furthermore, our analysis revealed the presence of subharmonics in the amplitude modulations of the second oscillator, abrupt transitions between harmonics, and distinct distortion products. These findings provide insights into the so far unknown mechanisms of sound production in this species. In addition, we draw comparisons with sound production mechanisms in other marine mammals and polyphonic phenomena in musical instruments.