以耳機實現3D立體環繞聲場

Abstract

3D多媒體聲場的重現早已成為市場上相當熱門的應用，本文提出一高效率合成頭部轉移函數之模型，以頭部轉移函數的特性及聲學理論為基礎，利用奇異值分解將頭部轉移函數之空間特性與時間特性分開。此模型之階數可以大幅降低並且導致運算效率有相當程度的提高。對於量測的頭部轉移函數資料庫離散的特性，此模型將內差法應用於分解後頭部轉移函數之空間成分，使得空間中任意位置的頭部轉移函數資料可以依照此模型快速而有效率的合成出來。我們針對此模型之效率作數值上的分析，可以發現此模型之運算效率與儲存空間之改善均隨著聲源個數的增加而提高。實際聽覺的定位實驗中，則驗證了降階之後的模型仍具有相當良好的定位效果。文末介紹了數個3D音效系統的實作技巧與應用，包含了微軟的DirectShow環境、Shuffler率波器架構、IIR率波器以及自行開發的各種PC上之應用軟體。

A functional model is presented for synthesizing Head-Related Transfer Functions (HRTFs) in three-dimensional audio reproduction. The spatial and temporal variations of HRTFs are separated, using the singular value decomposition (SVD). The order of the model can be reduced by using this method to yield significant enhancement of processing efficiency. Owing to the discrete nature of measured HRTFs, interpolation is performed on the spatial part of the model to result in finer resolutions. The HRTF at an arbitrary direction is represented as a weighted sum of the products of the spatial and temporal parts. Performance analysis of the algorithm reveals that the efficiency of this model considerably improves with increasing number of sound sources. Computational efficiency and storage requirement are assessed for HRTFs measured from a manikin. Subjective tests of sound source localization are also conduced. The results indicated the effectiveness of the proposed HRTF synthesis technique for both azimuth and elevation localization, without notable performance degradation. Numerous realizations of the immersive audio system are proposed. The Microsoft DirectShow technology and Windows operation system are used as the implementation environment. The efficiency of the realizations is increased by Shuffler filter arrangement and IIR approximation.