“…The most representative methods include some normalisation methods at the feature level, such as cepstral mean subtraction (CMS), H-norm, etc. (Wu et al, 2008) and transformation techniques at the feature level, such as LDA-based and NLDA-based feature transformation (Wu et al, 2005a(Wu et al, ,b,c, 2008. Processing at the model level then uses a variety of normalisation and transformation techniques at the model level that is a middle stage of a standard recognition system.…”