臺灣博碩士論文加值系統

由於聽覺感受是一種群體經驗，因此在多聲道音響系統等化器的設計上，各種聲學變因的考量是相當重要的一環。在多聲道系統中，聲音於密閉空間傳遞時，因各種不同路徑及反射訊號所造成的改變，均可使用空間轉移函數來描述，其中一種衡量空間轉移函數的方法，就是驗證其消除交叉與反射訊號的能力。為了實現上述功能之等化器，我們透過頭部相關轉移函數(HRTF)的特性，提出部份更新調適演算法，並將其引入到能夠有效抑制多聲道系統交叉項的最小均方(LMS)演算法中，由於HRTF已隱含空間音訊的條件，利用此關鍵因素的特性來建立系統模型將有助於降低非線性系統的複雜度。

另一方面，為使迴響空間聲場重建時有更佳的品質，除了選用無失真的揚聲器之外，在多聲道系統中，如何適當地選取高低音揚聲器間交越頻率，以呈現最佳化的頻譜，為音訊處理中另一重要課題。在本研究中，我們對於音響系統的交越頻率進行了相位補償，並利用最小化極大近似法使頻譜響應平坦化，以增強音訊在低頻頻段的效應，而採用串接式的全通濾波器，則能使高低音揚聲器之間頻譜的振幅響應於頻率交會處突顯出較補償前更加平坦的效果。最後，為佐證本方法的可行性，於迴響空間中錄音的數值分析也將一併提出。

As listening becomes a group experience, considering the acoustic variations in the design of equalizer for multichannel audio system turns out to be an indispensable process. The room transfer function describes the changes an audio signal undergoes when it propagates via a direct path and multipath reflections around an enclosed room. One of the criteria for a room transfer function design is to verify its capability of canceling indirect terms and multipath reflections. To perform such equalization, we propose a partial update adaptive algorithm based on the head-related transfer function (HRTF) and least-mean-square (LMS) approach to efficiently repress the indirect terms resulting from the multichannel playback system. Since HRTF has played a crucial role in the spatial audio signal processing, introducing this model is shown to facilitate the complexity reduction for a highly nonlinear system.

On the other hand, the selection of crossover frequency between the subwoofer and satellite loudspeakers is essential for reconstructing a nearly perfect sound field in the reverberation room. Apart from the distortion-free of individual loudspeakers, the overall spectral variation between the subwoofer and satellite loudspeakers should be minimized around the selected crossover frequency. In this work, we propose a phase compensation scheme based on the minimax approximation to flatten the spectral response around the crossover frequency for the loudspeaker system emphasized on the low-frequency effect. The cascaded all-pass filter is shown to yield an improved low-frequency performance by flattening the net magnitude response in the crossover region. As a result, several examples of numerical design based on the reverberant room recording are provided to verify the characteristics of the proposal systems.

摘要 i
Abstract ii
目錄 iii
圖片索引 v
專有名詞縮寫對照表 viii

第一章 導論 1
1.1 前言 1
1.2 多聲道音訊處理簡介 2
1.2.1 空間中高頻音訊分析 2
1.2.2 揚聲器低頻響應調校 3
1.3 本文架構 5

第二章 以調適濾波器分析人耳聲學系統 6
2.1 頭部相關脈衝響應 6
2.2 調適性多聲道系統 14
2.2.1 TDLMS調適演算法 15
2.2.2 FDLMS調適演算法 19

第三章 聲音訊號調適演算法應用 23
3.1 時頻域LMS演算法比較 23
3.1.1 以LPC對LMS演算法驗證 23
3.1.2 以白雜訊分析空間響應 25
3.1.3 空間反側音消除系統驗證 27
3.2 LMS部份更新演算法 32
3.2.1 FDLMS部份更新演算法 33
3.3 調適演算法之音訊分離應用 36

第四章 多聲道系統低頻響應相位補償 41
4.1 多聲道揚聲器音頻相位補償 42
4.2 基於最小化極大準則之FIR全通濾波器 44
4.3 以最小化極大近似法補償低頻響應相位 47

第五章 結論與未來展望 54
5.1 結論 54
5.2 未來展望 55

參考文獻 56

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