HHT-Based Time-Frequency Features in the Berardius Baird Whistles

This paper examined five Berardius Bairdii whistle samples and one referred sample, denoted as ws1(t), ws2(t), ws3(t), ws4(t), ws5(t), and rs1(t), respectively. McDonald, [1] recorded these samples in 1994 at 44° 16.1′ N, 130° 26.8′ W. The current study examined the Hilbert-Huang Transformation (HHT) based time-frequency features of the ws1(t), ws2(t), ws3(t), ws4(t), ws5(t), and rs1(t) samples. The ratios of the energy of the intrinsic mode function 1 (IMF 1) to the referred total energy of ws1(t), ws2(t), ws3(t), ws4(t), and ws5(t) were higher than that of the energy of IMF 1 to the referred total energy of the rs1(t). The energy ratio of IMF 3 to the referred total energy for ws1(t), ws2(t), ws3(t), ws4(t), and ws5(t) were lower than the IMF 3 to the referred total energy of rs1(t). The average energy ratio of IMF 1 to the referred total energy of the five Berardius Bairdii whistle samples in the 9–10, 10–11, 11–12, 12–13 and 13–14 kHz bands were 10.1141, 15.7863, 17.4510, 14.0474 and 5.2079 %, respectively. The average energy ratio of IMF 2 to the referred total energy of the five Berardius Bairdii whistle samples in the 4–5 and 5–6 kHz bands were 4.3647 and 15.9524 %, respectively. The energy ratios of IMF1 to the referred total energy of the rs1(t) sample in the 9–10, 10–11, 11–12, 12–13 and 13–14 kHz bands were 4.4015, 4.2476, 5.8980, 7.6276 and 8.7352 %, respectively. The energy ratios of IMF 2 to the referred total energy of the rs1(t) sample in the 4–5 and 5–6 kHz bands were 1.4801 and 1.9135 %, respectively. This study determined the correlations among the whistles in the HHT time-frequency characteristics, and obtained novel information on the vocal features of the Berardius Bairdii whistle .