1. An apparatus for determining a sequence of sub-word units representative of at least two words output by a word recognition unit in response to a common input word to be recognised, the apparatus comprising: means for receiving a first sequence of sub-word units representative of a first one of said at least two words and for receiving a second sequence of sub-word units representative of a second one of said at least two words; means for aligning and for comparing sub-word units of the first sequence with sub-word units of the second sequence to form a number of aligned pairs of sub-word units; and means for determining a sequence of sub-word units representative of the received words in dependence upon the aligned pairs of sub-word units determined by said aligning and comparing means.