1. Introduction  
2. Neural Vocoders  
2.1. WaveNet  
2.2. WaveRNN  
2.3. FFTNet  
2.4. Parallel WaveGAN  
3. Datasets and Evaluation Metrics  
3.1. Datasets for experiments  
3.2. Evaluation metrics  
4. Robustness to Human Speech  
4.1. Experimental setup  
4.2. Results  
5. The Influence of Genders  
5.1. Experimental setup  
5.2. Results  
6. Robustness to Speech Synthesis Task  
6.1. Experimental setup  
6.2. Results  
7. Conclusion