Tune frame length while training Tacotron?
Thank you for building a great open source project.

I'm trying to train Tarcotron using Korean datasets.

While training I just noticed that depending on `max_duration`, frame padding length will be changed, below images show `val_target` Mel spectrogram where `max_duration` is over 3.5sec and below 3.5sec. 

![image](https://user-images.githubusercontent.com/32811094/132269756-fceb2fc5-fab8-4b18-9a82-b8f22e8f8a82.png)

and I think it makes `valid_prediction` unstable. like the below images, Tacotron generates some noise at the end of a frame.

![image](https://user-images.githubusercontent.com/32811094/132270032-5b52f505-9cb9-4cdc-bc53-9cda5e29a83c.png)

Is there any way to tune this problem? or is it normal behavior for Tacotron?
