Speech recognition is a process that allows people to speak naturally to a computer on any topic and to be understood accurately. Speech is a form of communication we learn early and practice often, so the use of speech recognition software can simplify computer interfaces and make computers accessible to users unable to key text using a standard keyboard. However, computer-based speech recognition is more difficult to achieve than one might at first assume.

The speech recognition process is statistical in nature and is based on Hidden Markov Models (HMMs). An HMM is a finite set of states, each of which is associated with a probability distribution. Transitions among the states are governed by a set of probabilities called transition probabilities. The HMM is first trained using speech data for which the associated text is known. Subsequently, the trained HMM is used to "decode" new speech...