臺灣博碩士論文加值系統

本論文中，我們以基於注意力機制的卷積增強變換器 (Convolution-augmented Transformer, Conformer) 架構結合連續時序性分類來建立我們的端到端自動語音辨識 (Automatic Speech Recognition, ASR) 系統，同時使用上下文區塊處理 (Contextual Block Processing) 以及 逐塊同步集束搜索 (Blockwise Synchronous Beam Search) 的方法使系統可以達到串流 (Streaming) 的可能，並以此架構做為我們本文的基礎系統，後續基於此基礎系統我們採用 三種方法來提高自動語音辨識系統的性能。同時我們分別在各個系統上使用單語言以及語碼 轉換的資料集進行訓練以及利用遷移學習的方式微調系統，並使用單一語言以及語碼轉換測 試資料分別測試系統，並觀察改進後的系統在單語言以及語碼轉換情況下的結果。首先，我 們添加了一個對抗性文本鑑別器模塊對語音辨識模型進行訓練以糾正辨識結果中的拼寫錯 誤。實驗結果表明，加入對抗性文本鑑別器的單語言以及語碼轉換語音辨識系統的字符錯 誤率 (Character Error Rate, CER) 分別從 12.6% 以及 48.7% 下降至 12.3% 以及 45.1%，而 單詞錯誤率 (Word Error Rate, WER) 分別從 31.7% 以及 65.7% 下降至 31.4% 以及 65.4%。 其次，我們在語音辨識模型中加入了對應語言情境下的預訓練的語音合成 (Text to Speech, TTS) 模型。語音合成模型可以將語音辨識模型的輸出結果作為輸入以合成對應的梅爾頻譜 圖 (Mel-spectrogram)，並近似真實的 (Ground-truth) 梅爾頻譜圖。在加入了語音合成模型 後，單語言及語碼轉換的字元錯誤率分別從 12.6% 以及 48.7% 下降至 10.0% 以及 43.4%， 而單詞錯誤率分別從 31.7% 以及 65.7% 下降至 23.0% 以及 64.3%。這表明預訓練的語音合 成系統可以幫助提升語音辨識系統的效能。最後，我們將對應語言情境下的預訓練語音合成 模型和對抗性文本鑑別器合併並對語音辨識模型進行訓練。通過這樣做，不僅可以有效地 糾正錯別字，而且可以繼承語音合成系統修正原始語音辨識系統的效能。實驗結果表明，單一語言及語碼轉換的字符錯誤率與單詞錯誤率分別達到了 9.6% 和 22.0% 以及 41.6% 和 62.1%。

In this thesis, we implement our end-to-end automatic speech recognition system using the conformer architecture based on the attention mechanism and Connectionist Temporal Clas- sification, and we employed Contextual Block Processing and Blockwise Synchronous Beam Search towards real-time speech recognition, and this architecture has served as a baseline through the development of our system. The speech recognition system will be improved us- ing three methods based on this baseline. We train our systems using monolingual datasets and code-switching datasets. After training, we evaluate the improved system using monolin- gual and code-switching test data, and we observe how well they perform. First, we add an adversarial text discriminator module to train the speech recognition model to correct typos in recognition results. The experimental results show that the character error rates of the mono- lingual and code-switching speech recognition systems with text discriminators drop from 12.6% and 48.7% to 12.3% and 45.1%, respectively, and the word error rates from 31.7% and 31.7%, respectively. 65.7% down to 31.4% and 65.4%. Second, we added a pre-trained speech synthesis (text-to-speech, TTS) model to the ASR model for the corresponding lan- guage. TTS can synthesize the output of ASR into a mel-spectrogram and approximate the mel-spectrogram of the label. The character error rates for monolingual and code-switching dropped from 12.6% and 48.7% to 10.0% and 43.4%, respectively, while the word error rates dropped from 31.7% and 65.7% to 23.0% and 64.3%. Finally, we merge language-specific pre-trained TTS and an adversarial text discriminator to train the speech recognition model in different languages. By doing this, not only the typos can be corrected effectively, but also the advantages of pre-trained TTS can be inherited. According to the experimental results, the character error rate and word error rate of monolingual and code-switching are 9.6% and 22.0% and 41.6% and 62.1%, respectively.

目錄
論文審定書 i
誌謝 ii
摘要 iii
Abstract v
圖目錄 x
表目錄 xii
第 1 章 緒論 1
1.1 研究動機與目標 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 研究貢獻 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 投稿論文 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 文章架構 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
第 2 章 基礎端到端語音辨識系統 4
2.1 文本前處理模塊 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 資料增強 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 連續時序性分類 (Connectionist Temporal Classification) 模型 . . . . . . . . 7
2.4 注意力機制之介紹 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.1 變換器 (Transformer) 架構 . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.2 卷積增強變換器 (Conformer) 編碼器 . . . . . . . . . . . . . . . . . 14
2.5 結合連續時序性分類之端到端語音辨識系統 . . . . . . . . . . . . . . . . . . 15
2.5.1 訓練階段之損失函數 . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.5.2 解碼階段之計分方法 . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.6 實現串流處理之方法 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.6.1 應用於編碼器之上下文區塊處理方法 . . . . . . . . . . . . . . . . . . 18
2.6.2 用於解碼階段之逐塊同步集束搜索方法 . . . . . . . . . . . . . . . . 21
2.7 遷移學習方法 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
第 3 章 結合語音合成模型與對抗性文本鑑別器改進端到端語音辨識系統 25
3.1 對抗性文本鑑別器模塊 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2 利用對抗性文本鑑別器對語音辨識模型訓練之作法 . . . . . . . . . . . . . . 27
3.3 語音合成端到端模型 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3.1 文本轉拼音模塊 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3.2 可變資訊轉接器 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3.3 長度調節器 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.3.4 後網路架構 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3.5 語音合成模型之編碼器以及解碼器架構 . . . . . . . . . . . . . . . . 35
3.4 平滑動態時間校正 (Soft-Dynamic Time Warping, Soft-DTW) . . . . . . . . 36
3.5 利用語音合成模型加強語音辨識模型訓練之作法 . . . . . . . . . . . . . . . . 38
3.6 循環生成對抗網路架構 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.7 利用語音合成模型以及對抗性文本鑑別器對語音辨識模型進行訓練之作法 . . 44
第 4 章 實驗設置 46
4.1 語音辨識模型使用之資料集 . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.1.1 單語言資料集 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.1.2 語碼轉換資料集 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.1.3 FSR-2020 資料集 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2 語音合成模型使用之資料集 . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2.1 單語言資料集 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.2.2 多語言資料集 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.3 語音辨識模型以及語音合成模型之實驗設置 . . . . . . . . . . . . . . . . . . 49
第 5 章 實驗結果 52
5.1 語音辨識系統之評估方式 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.2 基礎語音辨識系統架構在單語言以及語碼轉換上的結果 . . . . . . . . . . . . 54
5.2.1 單語言測試集在單語言基礎語音辨識系統的結果分析 . . . . . . . . . 54
5.2.2 語碼轉換測試集在基礎語音辨識系統經過微調後的結果分析 . . . . . 55
5.3 利用對抗性文本鑑別器對語音辨識模型進行訓練之系統架構在單語言以及語碼轉換上的結果 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.3.1 單語言測試集在單語言對抗性文本鑑別器對語音辨識模型進行訓練之系統的結果分析 . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.3.2 語碼轉換測試集在對抗性文本鑑別器對語音辨識模型進行訓練之系統經過微調後的結果分析 . . . . . . . . . . . . . . . . . . . . . . . . 56
5.4 利用語音合成模型加強語音辨識模型訓練之系統架構在單語言以及語碼轉換上的結果 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.4.1 單語言測試集在單語言語音合成模型加強語音辨識模型訓練之系統的結果分析 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.4.2 語碼轉換測試集在語音合成模型加強語音辨識模型訓練之系統經過微調後的結果分析 . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.5 利用語音合成模型以及對抗性文本鑑別器對語音辨識模型進行訓練之系統架構在單語言以及語碼轉換上的結果 . . . . . . . . . . . . . . . . . . . . . . . 58
5.5.1 單語言測試集在單語言語音合成模型以及對抗性文本鑑別器對語音辨識模型進行訓練之系統的結果分析 . . . . . . . . . . . . . . . . . . 58
5.5.2 語碼轉換測試集在利用語音合成模型以及對抗性文本鑑別器對語音辨識模型進行訓練之系統經過微調後的結果分析 . . . . . . . . . . . 59
5.6 在語碼轉換情況效能低落之分析 . . . . . . . . . . . . . . . . . . . . . . . . 59
5.7 計算相似度的平滑動態時間校正與平均絕對誤差的比較 . . . . . . . . . . . . 59
5.8 FSR-2020 台文漢字實驗結果 . . . . . . . . . . . . . . . . . . . . . . . . . . 61
第 6 章 結論與未來展望 63
參考文獻 65

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