# Why are the observation features of an HMM-based recognition/synthesis system modeled by a Gaussian distribution?

Why are the observation features (namely MFCCs) of an HMM-based recognition/synthesis system modeled by a Gaussian distribution?

Even the state duration is modeled by a Gaussian in this paper:

K. Tokuda et al., "Speech synthesis based on hidden Markov models", Proceedings of the IEEE, May 2013