Airborne vs. radio-transmitted vocalizations in two primates: a technical report

Elucidating the structure and function of joint vocal displays (e.g. duet, chorus) recorded with a conventional microphone has proved difficult in some animals owing to the complex acoustic properties of the combined signal, a problem reminiscent of multi-speaker conversations in humans. Towards this goal, we set out to simultaneously compare air-transmitted (AT) with radio-transmitted (RT) vocalizations in one pair of humans and one pair of captive Bolivian grey titi monkeys (Plecturocebus donacophilus) all equipped with an accelerometer – or vibration transducer – closely apposed to the larynx. First, we observed no crosstalk between the two radio transmitters when subjects produced vocalizations at the same time close to each other. Second, compared with AT acoustic recordings, sound segmentation and pitch tracking of the RT signal was more accurate, particularly in a noisy and reverberating environment. Third, RT signals were less noisy than AT signals and displayed more stable amplitude regardless of distance, orientation and environment of the animal. The microphone outperformed the accelerometer with respect to sound spectral bandwidth and speech intelligibility: the sounds of RT speech were more attenuated and dampened as compared to AT speech. Importantly, we show that vocal telemetry allows reliable separation of the subjects’ voices during production of joint vocalizations, which has great potential for future applications of this technique with free-ranging animals.

针对部分动物而言，利用传统麦克风录制其联合发声行为（如二重唱、合唱）并阐明此类发声的结构与功能，由于组合信号复杂的声学特性，始终是一项颇具挑战的任务；这一难题与人类的多说话者对话场景颇为相似。为攻克这一难题，本研究旨在同时对比一对人类与一对圈养玻利维亚灰伶猴（*Plecturocebus donacophilus*）的空气传播（air-transmitted, AT）与无线电传播（radio-transmitted, RT）发声信号，所有受试对象均佩戴紧贴喉部的加速度计（accelerometer，或称振动传感器vibration transducer）。其一，当受试对象同时发声且彼此间距较近时，未观测到两台无线电发射器之间存在串扰现象。其二，相较于空气传播的声学录制结果，无线电传播信号的声音分段与基音追踪精度更高，在嘈杂混响环境中的优势尤为显著。其三，无线电传播信号的噪声水平低于空气传播信号，且无论受试动物的距离、朝向与所处环境如何，其振幅均更为稳定。在声音频谱带宽与语音清晰度方面，麦克风的表现优于加速度计：相较于空气传播语音，无线电传播语音的衰减与阻尼程度更高。尤为关键的是，本研究证实发声遥测技术可在联合发声过程中可靠分离各受试对象的发声信号，该技术在自由活动动物的后续研究与应用中具备巨大潜力。