Cepstral Mean and Variance Normalization (CMVN) is a computationally efficient normalization technique for robust speech recognition. The performance of CMVN is known to degrade for short utterances. This is due to insufficient data for parameter estimation and loss of discriminable information as all utterances are forced to have zero mean and unit variance.
References
Cepstral Mean and Variance Normalization Wikipedia(Text) CC BY-SA