An adaptive speech recognition system and method using a cascade of transforms

A speech processing method, comprising receiving a speech input in a first environment which comprises a sequence of observations, determining the likelihood of a sequence of words arising from the sequence of observations using an acoustic model and a language model, comprising providing an acoustic model for performing speech recognition on a input signal which comprises a sequence of observations, wherein said model has been trained to recognize speech in a second environment, said model having a plurality of model parameters relating to the probability distribution of a word or part thereof being related to an observation. The model trained in the second environment is adapted to that of the first environment. The speech recognition method further comprises determining the likelihood of a sequence of observations occurring in a given language using a language model, combining the likelihoods determined by the acoustic model and the language model and outputting a sequence of words identified from said speech input signal. Adapting the model trained in the second environment comprises using a cascade of transforms successively applied to the observations or model parameters, where a parent transform is a transform which is applied earlier in said succession of transforms, and a child transform is a transform applied later in the succession of transforms than said parent transform. The child transform is estimated on the basis of a prior transform and said prior transform is also said parent transform.