get_statistics_with_mask (mean vs sum)
Thank you for providing a very good framework and solution for speaker recognition.

To understand more about it, I read through source code and paper. I want to clarify one of the calculation in `get_statistics_with_mask`. To calculate statistics, the variable name and description is `mean` while the implementation is `sum`  when calculating input and mask.

May I confirm whether it is `mean` or `sum` operation? 

https://github.com/NVIDIA/NeMo/blob/v1.7.0/nemo/collections/asr/parts/submodules/tdnn_attention.py#L87