臺灣博碩士論文加值系統

本論文旨在提出一個能夠以類比電路實現的虛擬低頻演算法。在提出來的方法裡，吾人利用了聲音心理學理論去實現一個與傳統方法比較起來，能夠不需要額外的犧牲效益就能有效改善音訊低頻響應的演算法。體積小的喇叭與耳機擁有很差的頻率響應是一個眾所皆知的問題。在本論文中，首先提到一個運用虛擬音高產生基頻諧波去取代基頻的諧波產生器，以利完成新的演算法。而後根據等響度曲線圖去達成響度匹配的補償的機制。經過處理之後的低頻訊號成份再與原本的高頻訊號相加去取代原本的音訊，也就是所謂的虛擬低頻。在所提出的諧波產生器中，包括了遲滯比較產生器和半波整流器，去產生奇數與偶數個諧波。
本論文中也提出了一些類比電路所組成的簡單架構去實現所提出來
的演算法，其中包含了全波整流器，奇數與偶數諧波產生器；並且利用開關電容去取代大電阻實現濾波器。而詳細的驗證和效能將在稍後幾章中被描述。

The goal of this thesis is to propose a new algorithm of virtual bass with analog circuits realization. The proposed method utilized the technique of psycho-acoustic to enhance low frequency parts of the audio signals without other costs in contrast with conventional methods which have trade-off in some performances. Poor low frequency response of small size speakers and headphones is a well-known problem. In this thesis, a new algorithm with proposed harmonics generator is first presented that we make use of theorem of missing fundamental to generate harmonics of fundamental frequency and replace it. Then the compensation followed by equal-loudness contour analysis is made to achieve the technique of loudness matching. The processed low frequency components of audio signals are then added with original high frequency
components to replace the original audio signals. It is so-called virtual bass. The proposed harmonics generator includes a hysteresis comparison generator and a half-wave rectifier to generate odd and even harmonics.
We also propose some simple architecture composed of analog circuits to realize the proposed algorithm which include the proposed full-wave rectifier, odd harmonics
generator and even harmonics generator and use the switched-capacitor to replace the large resistance to realize filters. The detailed verification and performance will be described in the following chapters.

1.Introduction............................................1
1.1 Overview..............................................1
1.2 Background &Motivation................................1
1.2.1 Three-Dimension Enhancement.....................2
1.2.2 Treble Enhancement..............................2
1.2.3 Bass Enhancement................................3
1.3 Organization..........................................4

2 Fundamental of Psycho-acoustic Virtual Bass.............5
2.1 Overview..............................................5
2.2 The Association of Loudness and Sound Pressure Level
2.2.1 The Concept of Sound Pressure Level.............5
2.2.2 The Perception of Loudness......................8
2.3 Missing Fundamental................................. 11
2.3.1 Musical Notes and Their Fundamental Frequency..12
2.3.2 Musical Notes and Their Harmonics..............13
2.3.3 Pitch Perception Theory........................15
2.4 Processing Sound by Filtering........................17

3 System Design of Psycho-acoustic Virtual Bass..........22
3.1 Overview.............................................22
3.2 Equal-Loudness Contour Analysis......................22
3.3 Proposed Psycho-acoustic Algorithm...................27
3.3.1 Block Diagram..................................28
3.3.2 Concept of Hysteresis Comparison Generator.....32
3.3.3 Performance Summary............................40

4 Circuit Design of Psycho-acoustic Virtual Bass.........44
4.1 Overview.............................................44
4.2 Full-Wave Rectifier..................................44
4.3 Averaging Circuit....................................46
4.3.1 Concept of IIR Filter..........................46
4.3.2 Designing IIR Filter by Approximating Analog
Circuits.......................................48
4.3.3 Operation of Averaging Circuit.................49
4.4 Odd Harmonics Generator..............................50
4.5 Even Harmonics Generator.............................51
4.6 Non-inverting Amplifier..............................52
4.7 Operational Amplifier................................53
4.8 Switched Capacitor Filter............................56
4.8.1 Clock Generator................................57
4.8.2 Non-ideal Effects of Switches in SC Circuits...58
4.8.3 Switched Capacitor Low Pass Filter.............62
4.8.4 Switched Capacitor High Pass Filter................68
4.9 Comparator...........................................69

5 Verification and Measurement...........................71
5.1 Overview.............................................71
5.2 Simulation Results...................................71
5.2.1 Comparator.....................................71
5.2.2 Harmonics Generator............................73
5.2.3 Operational Amplifier..........................74
5.2.4 Switched Capacitor Filter......................75
5.3 Subjective Validation................................81
5.3.1 Testing Methods................................81
5.3.2 Testing Procedure............................. 82
5.3.3 Testing Results and Discussion.................84

6 Conclusion and Future Work.............................86

Reference................................................88

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