Speech recognition systems are utilized in many computer-based applications. For example, some mobile telephones are equipped with speech recognition systems that allow users of the mobile telephones to speak a name of a contact to be dialed, and the speech recognition system can recognize the spoken name from amongst a list of contacts of the user retained in the mobile telephone. The mobile telephone may then automatically dial the telephone number of the contact whose name was uttered by the user of the mobile telephone. In another example, some customer service applications accessible by way of a telephone can utilize speech recognition systems. For instance, the customer service application may be automated and may provide a user with several options. The user may then verbally utter a desired option, and the speech recognition system can recognize the selection of the user.
Various approaches have been undertaken in connection with performing speech recognition. For instance, generative models have been utilized in connection with performing speech recognition. In a generative model, first, information is known a priori on words or sequences of words that people are likely to speak (p(w)). For observations, the probability of such observations, given a certain word, can be modeled. A probability of the word (the prior) and the probability of the observations given the word can be utilized to determine a probability that the observations correspond to the word. Specifically, a word sequence that optimizes the combination of the probability of the word and the probability of certain observations given the word can be ascertained.
In another approach, direct modeling can be utilized in a speech recognition system. In the direct modeling approach, a model is utilized to model a probability of a word sequence given one or more observations without requiring the two separate computations described above pertaining to the generative model approach (the prior probability of word sequences and the probability of some observations given word sequences). Generative models can always output scores which can be used as features within the direct modeling framework.