自由场听觉距离感知因素的动态虚拟实验研究
An experimental investigation on cues of auditory distance perception in the free field based on dynamic virtual experiment
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摘要: 已有的物理分析和基于真实声源的实验研究表明, 响度和近场头相关传输函数(HRTF, 包括双耳声级差ILD和耳的声压谱)是自由场下听觉距离感知因素。但近年基于虚拟听觉重放(VAD)平台的相关实验结论却与此不一致, 特别是在近场HRTF中的ILD是否为自由场距离感知的重要因素问题上存在争议。为解决这些争议并进一步研究不同因素的贡献及其协同作用, 利用动态VAD平台和准确的近场HRTF合成的双耳声信号并使用耳机重放, 采用心理声学实验研究了距离感知因素。结果表明, 首先不同距离感知因素的贡献与声源的方向有关: (1) 响度因素在所有方向都有重要贡献; (2) ILD主要在侧向有重要贡献, 其贡献随着声源向前、后或高仰角偏离侧向而减少; (3) 谱是较弱的因素, 只有在中垂面ILD为零时才有可能检测到其贡献。其次, 不同因素间存在协同交互作用和一定冗余: (1) 响度与ILD的交互作用明显增强侧向距离感知; (2) 响度与谱因素交互作用一定程度上增强后方的距离感知; (3) 单一的ILD或响度可在一定程度上产生侧向距离感知。近年距离感知研究中的争议主要是因为这些实验是在稳态VAD平台上进行的, 稳态VAD容易引起头中定位, 影响距离感知; 同时不准确的近场HRTF数据、不合适的实验方法与数据统计也会导致不一致的实验结论。Abstract: Previous physical analysis and experiments with real sound source indicated that loudness and near-field head-related transfer functions (HRTFs, including interaural level difference ILD and pressure spectra at ears) are cues for auditory distance perception in the free filed. However, recent experiments conducted on the platform of virtual auditory display (VAD) have yielded inconsistent results, especially regarding the controversy over whether ILD in near-field HRTF is a crucial cue on distance perception in the free field. This work aims to settle the controversy and further investigate the contribution and interaction of various distance perception cues in the free field. Based on a platform of dynamic VAD and accurate near-field HRTFs, binaural signals under different conditions are synthesized and presented by headphone, and the contributions of distance perception cues are then identified by psychoacoustic experiments. Firstly, results indicate that the contributions of various distance perception cues depend on source direction: (1) Loudness contributes significantly to distance perception in all directions; (2) ILD contributes importantly at lateral directions. Contribution of ILD reduces as source departs from lateral to the frontal, back or high-elevation directions; (3) Spectral cue contributes weakly to distance perception. Only in the median plane where the ILD vanishes may the contribution of spectral cue be detected. Secondly, different cues interact with one another but are somewhat redundant: (1) The coordination of ILD and loudness obviously enhances distance perception at lateral directions; (2) The coordination of loudness and spectral cue enhances distance perception at rear direction to some extent; (3) ILD or loudness alone enables to moderately distance perception at lateral direction. The controversy on the results of some recent experiments is due to the fact that these experiments were conducted on the platform of static VAD, which were inclined to cause in-head localization and influence distance perception. Moreover, inaccurate near-field HRTF data, inappropriate experimental and statistical methods may also cause inconsistent results.