Editing Carnegie Mellon's Harpy System (section)

=== Dragon System<ref name=":0">Lowerre, B. T. (1976). ''The HARPY Speech Recognition System''. Department of Computer Science, Carnegie-Mellon University.</ref> ===

*'''The Dragon system''' is interesting for its simplicity of design, mathematical tractability and high accuracy performance, which can achieve 100% accuracy on a set of speech data using only '''syntactic and acoustic-phonetic knowledge''';
*It achieves recognition by updating state probabilities of a '''Markov network'''. All possible paths are searched in parallel by a '''dynamic programming scheme''' and lead through states representing all syntactic and phonetic pronunciations;
*The most significant feature of the system is that it '''contains no coded heuristics''' except for the '''acoustic probability matching routine'''. It shows that there is a search algorithm which guarantees a recognition and in a deterministic amount of time.

{| class="wikitable"
|+
!
!Hearsay-I System
!Dragon System
|-
|Model 
|cooperating parallel process
|probabilistic function of Markov Process 
|-
|knowledge representation
|Procedures 
|Markov Networks
|-
|Unit of Speech 
Signal Representation  
|segmentation 
|10 milli-second sample 
|-
|search strategy 
|best-first 
|all paths in parallel
|-
|search time 
|8-50 times real-time
|45-200 times real-time
|-
|What Have Been Tested
|144 connected utterances 
676 words  

5 speakers 
 
4 tasks: Chess, News Retrieval, Medical Diagnosis, Desk Calculator  

28-76 word vocabularies 
|102 utterances
564 words<ref name=":1">Lowerre, B. T. (1974). Comparison of Two Speech Understanding Systems. ''The Journal of the Acoustical Society of America'', ''56, S27''. <nowiki>https://pubs.aip.org/asa/jasa/article/56/S1/S27/740227/Comparison-of-two-speech-understanding-systems</nowiki></ref>
|-
|Performance
|<u>Percentage of words spotted and identified correctly</u> <ref>Reddy, R. (2013). ''CMU Hearsay 1973 (Short Version)''. Retrieved September 17, 2023, from <nowiki>https://www.youtube.com/watch?v=c70QlwttnVg</nowiki>.</ref> 
89% with all the sources of knowledge 

67% without semantics 

44% without syntax and semantics 

(as of October, 1973)
|85% of the words identified correctly<ref name=":1" />
|-
|Approaches 
|acoustics-phonetics, prosody, lexicon, syntax, semantics and pragmatics
|Treats speech recognition as a mathematical computation problem
rather than as an artificial intelligence problem. 
|}