Editing Carnegie Mellon's Harpy System (section)

==== 5.3 State Size reduction ====
The recognition time is dependent upon the confusability among the paths in the Harpy system. The developers removed '''null states, redundant states''', and subsumed '''common states''' to reduce the network size and complexity. The former two removals have no effect on speech recognition accuracy, while the last removal has the potential influencing the recognition process.

* A null state is a state contains no synthetic or phonetic information other than the connections to its prior and following states. Harpy removes null states by linking each of it prior states to each of its following states and deleting the null states. However, the removal of null states increases the number of pointers.
* Two redundant states are 1) same terminal lexical symbol and same prior states or 2) same terminal lexical symbol and same following states. One of the states is selected and removed by Harpy.
* Two states are common if they both have the same phone and 1) same prior states or 2) same following states. Similarly, one state is selected and removed. To avoid danger of completely losing grammatical information due to subsumption of homonyms, the special character ‘!’ may use in the acoustic dictionary to indicate the network compiler.