頭相關轉移函數量測及含有殘響之三度空間聲音合成

Abstract

頭相關轉移函數(Head Related Transfer Function)為現今三度空間音效合成及處理之趨向。此函數描述來自不同方向的聲音事件經過聽者頭顱，外耳及身體的反射而在時域及頻域上的改變。一般而言，此函數以方向為變量，考慮在無迴響環境(Free Field)內的聲音事件當中的直接聲波(Direct Sound)之改變。本研究旨在量測此函數，並進一步考慮聲音事件的距離變化對於此函數的影響，以及在一般有迴響環境(Diffuse Field)的聲音事件中，非直接聲波(Indirect Sound)對於空間聽覺的交互影響。 本篇論文研究結果包括：一.於有迴響環境中建構一套完整並有效的HRTF量測程序。二.利用人頭模型建立遠場及近場頭相關轉移函數(Far Field and Near Field HRTF)及其所對應的雙耳空間脈衝響應函數(Binaural Room Impulse Response)資料庫,並討論來自不同方向及水平面上不同距離所產生的特徵變化。三.對於近場及遠場函數分別建構兩個圖像式使用者介面(Graphical User Interface)檢視量測結果，以探討其所描述的方向線索(Directional Cues)及距離線索(Distance Cues)。四.建立遠場及近場音效合成運算架構，利用遠場函數加入非直接聲波，雙耳角度差，殘響╱直接聲波之聲壓比等條件，以探討利用遠場函數合成近身音源的可能性。

Head Related Transfer Function (HRTF) is one of the major topics in 3D audio processing. This function describes the change both in time and frequency domain when a sound event comes from different direction being reflected by head, pinna and torso of the listener. This study intends to measure the transfer function with considerations on the influence of the distance of sound source and the indirect sound in a common diffuse field. The main purposes of this thesis are: (1) Construct a through and effective HRTF measurement process in a reverberant environment. (2) Measure both Far Field and Near Field HRTF and its associated Binaural Room Impulse Response (BRIR). Study the changes in directional and distance cues at different distance and direction in the horizontal plane. (3) Design and Implement two HRTF analysis and synthesis platforms with friendly Graphical User Interfaces (GUI) to use the content of database. (4) Propose two algorithms to synthesize Near Field and Far Field spatialized sound. Discuss the possibility of synthesizing the Near Field spatialized sound based on the Far Field HRTF with proper cues such as indirect sound, auditory parallax, and reverberation/direct sound pressure level.