Isolated recognition in general means recognition of speech based on
any kind of isolated speech unit, which can be a word or a sub word
or even a concatenation of words. However only isolated word
recognition has direct practical applications, while the isolated recognition
based on other two types of units has basically a theoretical value.
Specially the sub word recognition in isolated mode can give a good
indication about the continuous recognition based on the same
In a simple isolated speech unit recognition task, where the vocabulary contains N speech units, we can use the system depicted in fig.1.1.
Figure 1.1: A simple isolated speech unit recognizer
There are however many possible solutions to the task, because we have
many choices of optimization criteria, and several algorithmic
implementations even for a particular criterion. Out of those, a
gradient based method with MMI criterion will be described below.
Of course the task is comprised of two sub tasks; namely the training and recognition.