電腦音樂是一個跨資訊工程及音樂藝術結合的領域。此篇論文中我們將以可變動長度基因演算法來實現電腦自動伴奏。讓所有人都可以透過我們實作的系統自動做出符合自己需求的音樂伴奏。我們針對流行音樂分析節奏、和弦、主旋律三個重要的音樂特色，提出對應的染色體編碼方式做具體表現，並且將和弦之間行進的觀念融入基因演算法的評估之中。
本系統可供使用者輸入主旋律並選取情緒及節奏，系統將根據和旋行進相關樂理所建立之資料庫以自動化方式產生適合的伴奏。此外本系統能讓使用者自行選擇較喜歡的伴奏,並根據使用者喜歡的伴奏產生相似的伴奏呈現給使用者。

The domain of computer music is an interesting area which combines computer science and music art. We propose a music accompaniment system using a variable-length genetic algorithm. Via the system one can make the music corresponded to his demands. In the style music accompaniment we analyze some important characteristic of pop music, and propose a new chromosome representation scheme to include the concept of rhyme, chord and melody. Chord progression is used as one of the evaluation criterions in this thesis.
The system allows a user to input melody, to select emotion and rhyme, and the system will automatically generate the appropriate accompaniment based on the database compiled from some music theory relating to the chord progression. In addition, the system allows a user to select his favorite accompaniment that generated by the system. Based on the user selected accompaniment the system will generate similar accompaniments for the user.

Contents
Chapter 1 Introduction 1
Chapter 2 Background Materials and Literature Review 3
2.1 Background Materials 3
2.1.1 Music Domain Knowledge 3
2.1.2 Genetic Algorithm and the Variable-Length Scheme 5
2.2 Literature Reviews 6
Chapter 3 Problem Definition 9
3.1 Problem Statement 9
3.2 The Pop Song Constraints in Composition 11
3.3 Data Structure and Chromosome Representation 12
Chapter 4 The Proposed Algorithm 16
4.1 The Factors for Interactive Mechanism 17
4.2 The Variable-Length Genetic Algorithm with Interactive Mechanism 18
4.2.1 Initialization 19
4.2.2 Evaluation 25
4.2.3 Selection 29
4.2.4 Crossover with the Variable-Length Scheme 29
4.2.5 Mutation 32
4.2.6 Elimination 33
Chapter 5 Implementation 34
Chapter 6 Conclusions 39
References 40

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