以Up/Downmix和CCS實現3D立體環繞音效於雙聲道喇叭

Abstract

本論文的研究著重於實現雙聲道喇叭的三度空間立體音效。頭部轉移函數(HRTF)和串音消除系統(CCS)是實現立體環場音效的核心技術，經由頻域和時域兩種解摺積(Deconvolution)方法可以計算出來串音消除系統所需的逆濾波器，其中正規化(Regularization)的處理以及逆濾波器實現架構的設計也都是重要的考量。另外，本文提出了兩個修正的串音消除系統設計方法來改善立體音效的重現。另一方面，upmix和downmix技術在許多的多媒體產品中扮演著相當重要的角色，當提供的音訊內容或播放系統的聲道受到限制時，藉由upmix和downmix的技術可以產生出多聲道的音場重現，各種不同的upmix和downmix方法將在本文中介紹。以上所提出的技術將在本文中進行主觀以及客觀的實驗評估，最後經由實驗結果可提供最佳化的三度空間立體音效設計方法。

This dissertation focuses on the 3D audio reproduction for two-channel stereo loudspeakers. To create spatial impression during audio reproduction, the head-related transfer function (HRTF) and the crosstalk cancellation system (CCS) are key elements in many audio spatializers. Two deconvolution approaches, the frequency-domain method and the time-domain method, are employed to design the required inverse filters. Different approaches to design audio spatializers with the HRTF, CCS, and their combination are compared. Issues in the implementation phase such as regularization, complex smoothing and structures of inverse filters are also addressed. In particular, two modified CCS approaches are proposed. In addition, upmix and downmix processing plays an important role in many audio applications, where the number of channels of either the audio content or the reproducing loudspeakers are limited. Various upmix and downmix methods are presented in this work. A comprehensive study is undertaken, by comparing a variety of the proposed approaches, to find guidelines and strategies for 3D audio technique to meet the ever increasing needs of multichannel stereophonic systems. All proposed methods were examined both objectively and subjectively, and had been proven to be effective in 3D audio reproduction.