1. A method of adapting an acoustic model for use in a speech recognition engine, comprising: subspace coding the acoustic model by a computer to obtain a plurality of codebooks each including a plurality of codewords, the plurality of codebooks including at least one codebook per subspace. adapting the codewords in the codebooks based on adaptation training data, by applying an adaptation transform to the codewords, regardless of whether the acoustic model is recomputed based on the adaptation training data.