This preview shows pages 1–5. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Massachusetts Institute of Technology Department of Electrical Engineering & Computer Science 6.345/HST.728 Automatic Speech Recognition Spring, 2010 4/15/10 Lecture Handouts FiniteState Transducers (FSTs) Reading: Garner, A weighted finite state transducer tutorial Mohri, Finitestate transducers in language and speech processing (op tional) Homework: Assignment 5: FiniteState Transducers MIT FiniteState Transducers for Speech Recognition Introduction Basics Finitestate acceptor (FSA) Finitestate transducer (FST) Deterministic FSA/FST Weighted FSA/FST FSA/FST operations Closure , union , concatenation, intersection, epsilon removal, determinization, minimization, composition Speech Recognizers Construction via composition of FSTs Phone/word graphs & confusion networks Successive Search 6.345/HST.728 Automatic Speech Recognition (2010) FiniteState Transducers 1 MIT Introduction Many ASR components can be represented as finitestate machines ngram language models Dictionaries Phonological rules (dictionary expansion) Nbest lists ... By representing all components as finitestate machines, we can Take advantage of powerful finitestate algorithms Implement algorithms once, use them everywhere Maintain consistency and flexibility to combine components in new ways Use of FSTs in ASR was pioneered by AT&T researchers [Pereira, Riley, Ljolje, Mohri, et al.] 6.345/HST.728 Automatic Speech Recognition (2010) FiniteState Transducers 2 MIT FiniteState Acceptor (FSA) a b 1 2 a 3 b accepts ( a  b ) ab Finite set of states; one initial, at least one final. Arc labels are drawn from alphabet . is the null label. Can be viewed as an acceptor or generator of strings. Accepts/generates a regular language. 6.345/HST.728 Automatic Speech Recognition (2010) FiniteState Transducers 3 MIT FiniteState Transducer (FST) a:b b:a 1 : 2 a: 3 :a e.g., ( aba ) a ( bab ) a Like FSA, but arc labels are pairs of input:output symbols. on input consumes no input. on output generates no output. Can be viewed as generating pairs of strings, accepting pairs of strings, or transducing from input strings to output strings. An FST with labels x : x is equivalent to an FSA. 6.345/HST.728 Automatic Speech Recognition (2010) FiniteState Transducers 4 MIT FSAs/FSTs with Weights 1 a/0.6 a/0.4 2/0.5 b/0.7 b/0.3 Arcs and final states can have weights (costs or scores) Behavior of weights is defined by a semiring ( , , , 1 ) defines how parallel path costs are combined....
View
Full
Document
 Spring '10
 Glass
 Computer Science

Click to edit the document details