1 INTRODUCTION

2 BACKGROUND  
2.1 Background on audio and speech  
2.2 Background on diffusion model  

3 TEXT-TO-SPEECH SYNTHESIS  
3.2 Acoustic model  
3.3 Vocoder  
3.4 End-to-end frameworks  

4.1 Enhancement by removing  
4.2 Enhancement by adding  
4.3 Miscellaneous audio tasks  

5 CONCLUSION