Hansen M, Wahlberg M, Madsen P T
Department of Biological Sciences, University of Aarhus, Denmark.
J Acoust Soc Am. 2008 Dec;124(6):4059. doi: 10.1121/1.2945154.
Underwater sound signals for biosonar and communication normally have different source properties to serve the purposes of generating efficient acoustic backscatter from small objects or conveying information to conspecifics. Harbor porpoises (Phocoena phocoena) are nonwhistling toothed whales that produce directional, narrowband, high-frequency (HF) echolocation clicks. This study tests the hypothesis that their 130 kHz HF clicks also contain a low-frequency (LF) component more suited for communication. Clicks from three captive porpoises were analyzed to quantify the LF and HF source properties. The LF component is 59 (S.E.M=1.45 dB) dB lower than the HF component recorded on axis, and even at extreme off-axis angles of up to 135 degrees , the HF component is 9 dB higher than the LF component. Consequently, the active space of the HF component will always be larger than that of the LF component. It is concluded that the LF component is a by-product of the sound generator rather than a dedicated pulse produced to serve communication purposes. It is demonstrated that distortion and clipping in analog tape recorders can explain some of the prominent LF components reported in earlier studies, emphasizing the risk of erroneous classification of sound types based on recording artifacts.
用于生物声纳和通信的水下声音信号通常具有不同的声源特性，以实现从小物体产生高效声反向散射或向同种个体传递信息的目的。港湾鼠海豚（Phocoena phocoena）是不发出啸声的齿鲸，会发出定向、窄带、高频（HF）回声定位咔哒声。本研究检验了这样一个假设，即它们130千赫的高频咔哒声中还包含一个更适合通信的低频（LF）成分。对三只圈养鼠海豚发出的咔哒声进行了分析，以量化低频和高频声源特性。低频成分比轴向上记录的高频成分低59（标准误=1.45分贝）分贝，即使在高达135度的极端离轴角度下，高频成分也比低频成分高9分贝。因此，高频成分的有效空间总是大于低频成分的有效空间。研究得出结论，低频成分是声音发生器的副产品，而不是为了通信目的而产生的专用脉冲。研究表明，模拟磁带录音机中的失真和削波可以解释早期研究中报道的一些突出低频成分，强调了基于记录伪像对声音类型进行错误分类的风险。
