近年來，文字轉語音的合成音質已有顯著的提升，然而在自然度的表現上，仍有很大的進步
空間。主要是因為合成語音多為中性語氣，欠缺個人說話特色或者自然的感情流露。因此，開啟
了表達式語音合成的研究，以期提升合成語音的自然度。目前已有相當多的文獻探討如何開發基
於表達式語音合成的文字轉語音系統。本論文提供了完整的回顧並歸納出五個研究主題
─說話方式, 情緒分類, 語料庫建構, 表達式語音合成方法以及合成語音評比。

In recent years the quality of the speech generated by text-to-speech synthesis has been improved dramatically. However the naturalness of the synthesized sound can be further improved to have more emotions to imitate human kind speaking. This inspires the research of expressive speech synthesis (ESS) to improve naturalness. Currently, there have been a lot of papers focusing on the development of ESS based text-to-speech systems. This study tries to give an overview of ESS studies and summarize five research topics ─ speaking styles, emotion categories, corpus construction, ESS approaches, and the evaluation of
synthetic sounds.