Naguib Marc
Department of Animal Behavior, University of Bielefeld, P.O. Box 100 131, 33501 Bielefeld, Germany.
J Acoust Soc Am. 2003 Mar;113(3):1749-56. doi: 10.1121/1.1539050.
Many acoustic signals in animals include trills, i.e., rapid repetitions of similar elements. Elements within these trills usually are frequency modulated and are degraded by reverberation during long-range transmission. Reverberation primarily affects consecutive elements with the same frequency characteristics and thus imposes a major constraint in the evolution of design and perception of long-range signals containing trills. Here transmission of frequency-unmodulated trills with different element repetition rates was studied. Trills were generated at different frequencies to assess frequency dependence of reverberation and then broadcast under three acoustic conditions--an open field and to assess seasonal changes in transmission properties, a deciduous forest before and after foliage had emerged. Reverberation was quantified at different positions within trills. The results show strong effects of vegetation density (season), transmission distance, frequency, element repetition rate, and element position within the trill on effects of reverberation. The experiments indicate that fast trills transmit less well than slow trills and thus are less effective in long-range communication. They show in particular that selection on trills should not act only on element repetition rate within trills but also on the trill duration as effects of reverberation increased with trill duration.
动物中的许多声学信号都包含颤音，即相似元素的快速重复。这些颤音中的元素通常是频率调制的，并且在远距离传输过程中会因混响而衰减。混响主要影响具有相同频率特征的连续元素，因此在包含颤音的远距离信号的设计和感知进化中构成了主要限制。在此，研究了具有不同元素重复率的非频率调制颤音的传输。在不同频率下产生颤音以评估混响的频率依赖性，然后在三种声学条件下进行广播——一个开阔场地以及一片落叶林在树叶出现前后，以评估传输特性的季节性变化。在颤音内的不同位置对混响进行量化。结果表明，植被密度（季节）、传输距离、频率、元素重复率以及颤音内元素的位置对混响效果有强烈影响。实验表明，快速颤音的传输效果不如慢速颤音，因此在远距离通信中效果较差。它们特别表明，对颤音的选择不应仅作用于颤音内的元素重复率，还应作用于颤音持续时间，因为混响的影响会随着颤音持续时间的增加而增加。
