The importance of the information in the direct sound to human perception of spatial sound sources is an ongoing research topic. The classification between direct sound and diffuse or reverberant sound forms the basis of numerous studies in the field of spatial audio. In particular, parametric spatial audio representation methods use this classification and employ signal processing in order to enhance the audio quality at reproduction. However, current literature does not provide information concerning the impact of ideal direct sound representation on externalization, in the context of Ambisonics. This paper aims to assess the importance of the spatial information in the direct sound in the externalization of a sound field when using binaural reproduction. This is done in the spherical harmonics (SH) domain, where an ideal direct sound representation within an otherwise Ambisonics signal is simulated, and its perceived externalization is evaluated in a formal listening test. This investigation leads to the conclusion that externalization of a first order Ambisonics signal may be significantly improved by enhancing the direct sound component, up to a level similar to a third order Ambisonics signal.

翻译：直接声信息对人类感知空间声源的重要性是一个持续的研究课题。直接声与扩散声或混响声的区分构成了空间音频领域众多研究的基础。特别是，参数化空间音频表示方法利用这种区分，并通过信号处理来提升重放时的音频质量。然而，当前文献并未提供关于在Ambisonics背景下理想直接声表示对外化影响的信息。本文旨在评估在使用双耳重放时，直接声中的空间信息对声场外化的重要性。研究在球谐函数域中进行，模拟了Ambisonics信号中理想直接声表示，并通过正式听音测试评估其感知外化效果。研究得出结论：通过增强直接声分量，一阶Ambisonics信号的外化效果可显著提升，达到与三阶Ambisonics信号相似的水平。