Relationship among phoneme/word recognition rate, perplexity and sentence recognition and comparison of language models

An evaluation technique is very important for developing a successful continuous speech recognition system. The branching factor and the perplexity have been used to measure the complexity of speech recognition task. The authors describe their evaluation method, which is based on such a measure. They found the relationship among perplexity ( V_p) on word-unit (or phoneme-unit), sentence length (L), word (or phoneme) recognition rate (R_w), and sentence recognition rate. From this relationship, they can predict the sentence recognition rate, if the word (or phoneme) recognition performance and task definition are given. The approximate equation is as follows: sentence recognition rate={f (V_p, R_w)}^L, where f(V_p,R_w) denotes the word recognition rate for the vocabulary size V_p obtained by using this recognizer (R_w) and this is estimated from the relationship between the number of categories and recognition rate