Progress of Sphinx 3.X, From X=4 to X=5 By Arthur Chan Evandro Gouvea Yitao Sun David Huggins-Daines Jahanzeb Sherwani

What is CMU Sphinx? Definition 1 : a large vocabulary speech recognizer with high accuracy and speed performance. Definition 2 : a collection of tools and resources that enables developers/researchers to build successful speech recognizers

Brief History of Sphinx More detail version can be found at, Sphinx I 1992 Sphinx II 1996 Sphinx III “S3 slow” 1999 Sphinx III “S3 fast” or S Sphinx become open-source Sphinx IV Development Initiated -S Jul S Oct S3.5 RCII

What is Sphinx 3.X? An extension of Sphinx 3’s recognizers “Sphinx 3.X (X=5)” means “Sphinx 3.5” It helps to confuse people more. Provide functionalities such as Real-time speech recognition Speaker adaptation Developers Application Interfaces (APIs) 3.X (X>3) is motivated by Project CALO

Development History of Sphinx 3.X S3 -Sphinx 3 flat- lexicon recognizer (s3 slow) S3.2 -Sphinx 3 tree-lexicon recognizer (s3 fast) S3.3 -w live-mode demo S3.4 -fast GMM computation -support class-based LM -some support for dynamic LM S3.5 –some support on speaker adaptation -live mode APIs -Sphinx 3 and Sphinx 3.X code merge

This talk A general summary of what’s going on. Less technical than 3.4 talk Folks were so confused by jargons in speech recognition’s black magic. More for code development, less for acoustic modeling Reason: I have not much time to do both (Incorrect version): “We need to adopt the latest technology to clown 2 to 3 Arthur Chan(s) for the CALO project.” –Prof. Alex Rudnicky, in one CALO meeting in 2004 (“Kindly” corrected by Prof. Alan Black): “We need to adopt the latest technology to clone 2 to 3 Arthur Chan(s) for the CALO project.” –Prof. Alex Rudnicky, in one CALO meeting in 2004 More on a project point of view Speech recognition software easily shows phenomena described in “Mythical Man-Month”.

This talk (outline) Sphinx 3.X, The recognizer (From X=4 to X=5) (~10 pages) Accuracy and Speed (5 pages) Speaker Adaptation (1 page) Application Interfaces (APIs) (2 pages) Architecture (2 pages) Sphinx as a collection of resources (~10 pages) Code distribution and management (3 pages) Infrastructure of Training (1 page) SphinxTrain: tools of training acoustic models. (1 page) Documentation (3 pages) Team and Organization (2 pages) Development plan for Sphinx 3.X (X >= 6) (2 pages) Relationship between speech recognition and other speech researches. (4 pages)

Accuracy and Speed Why Sphinx 3.X ? Why not Sphinx 2? Due to the limitation of computation in 90s S2 only support restricted version of semi-continuous HMM (SCHMM) S3.X supports fully continuous HMM (FCHMM) Accuracy improvement is around relative 30% You will see benchmarking results two slides later Speed S3.X is still slower than S2 But in many tasks, it seems to becomes reasonable to use it. (YOU CAN FIND THE RESULTS FEWS SLIDES)

Speed Fast Search techniques Lexical tree search (s3.2) Viterbi beam tuning and Histogram beam Pruning(s3.2) Ravi’s talk Phoneme look-ahead (s3.4 by Jahanzeb) Fast GMM computation techniques (s3.4) Using the measurement in the literature, that means 75%-90% of GMM computation reduction with fast GMM computation + pruning. <10% relative degradation can usually be achieved in clean database. Further Detail: “Four-Layer Categorization Scheme of Fast GMM Computation Techniques“ A. Chan et al.

Accuracy Benchmarking (Communicator Task) Test platform, 2.2G Pentium IV CMU Communicator task Vocabulary size (3k), perplexity: ~90 All tunings were done without sacrificing 5% performance. Batch mode decoder is used. (decode) Sphinx 2 (tuned w speed-up techniques) WER: 17.8% (0.34xRT) Baseline results Sphinx 3.X 32 gaussian-FCGMM WER: % (2.40xRT) Baseline results Sphinx 3.X, 64 gaussian-FCGMM WER: 11.7% (~3.67xRT) Tuned Sphinx 3.X 64 gaussian-FCGMM WER: % (0.87 xRT), % (1.17xRT) Rong can make it better: Boosting training results : 10.5%

Accuracy/Speed Benchmarking (WSJ Task) Test platform, 2.2G Pentium Vocabulary Size (5k) Standard NVP task. Trained by both WSJ0 and WSJ1 Sphinx 2, 14.5% (?) Sphinx 3.X, 8 gaussian-FCGMM un-tuned 7.3% 1.6xRT tuned: 8.29% 0.52xRT

Accuracy/Speed Benchmarking (Future Plan) Issue 1 : Large variance in GMM computation. Average performance is good, worse case can be disastrous. Issue 2 : Tuning requires a black magician Automatic tuning is necessary. Issue 3 : Still need to work on larger databases (e.g. WSJ 20k, BN) training setup need to be dig up Issue 4 : Speed up in noisy corpus is tricky. Results are not satisfactory (20-30% degradation in accuracy)

Speaker Adaptation Start to support MLLR-based speaker adaptation y=Ax+b, estimate A, b in a maximum likelihood fashion (Legetter 94) Current functionality of sphinx 3.X + SphinxTrain Allow estimation of transformation matrix Transforming means offline Transforming means online Decoder only support single regression class. Code gives exactly the same results as Sam Joo’s code. Not fully benchmarked yet, still experimental

Live-mode APIs Thanks to Yitao Sets of C APIs that provide recognition functionality Close to Sphinx 2’s style of APIs Speech recognition resource initialization/un-initialization Functions for Utterance level begin/end/process waveforms

Live-mode APIs : What are missing? What we lack Dynamic LM addition and deletion part of the plan of s3.6 Finite state machine implementation part of plan of s3.X where X=8 or 9 End-pointer integration and APIs Ziad Al Bawab’s model-based classifier Now as a customized version, s3ep

Architecture “Code duplication is the root of many evils” Four tools of s3 are now incorporated into S3.5 align : an aligner allphone : a phoneme recognizer astar : lattice to N-best generation dag : lattice best-path search Many thanks to Dr. Carl Quillen of MIT Lincoln

Architecture : Next Step decode_anytopo will be the next Things we may incorporate someday SphinxTrain CMU-Cambridge LM Toolkit lm3g2dmp and cepview

Code Distribution and Management Distribution Internal Release -> RC I -> RC II.. -> RC N If no one yell during calm-down period of RC N Then, put a tar ball on Sourceforge web page At every release, Distribution have to go through ~10 platforms of compilation First announcement usually made at the RC period. Web page is maintained by Evandro (<-extremely sane)

Digression: Other versions of Sphinx 3.X Code that are Not satisfying design goal of the software S3 slow w/ GMM Computation S3.5 with end-pointer CMU Researchers’ code and implementation E.g. According to legend, Rita has >10 versions of Sphinx and SphinxTrain.

Code Management Concurrent Versions System (CVS) is used in Sphinx Also used in other projects e.g. CALO and Festival A very effective way to tie resource and knowledge together Problems : Still has a lot of separate versions of code in CMU not in Sphinx’s CVS. Please kindly contact us if you work on something using Sphinx or derived from Sphinx

Infrastructure of Training A need for persistence and version control Baseline were lost after several years. setup will be now available in CVS for Communicator (11.5%) WSJ 5k NVP (7.3%) ICSI Phase 3 Training Far from the state of the art Need to re-engineer and do archeology Will add more tasks to the archive You are welcomed to change the setup if you don’t like it But you need to check in what you have done

SphinxTrain SphinxTrain is never officially released Still under work. For sphinx3.X (X>=5), corresponding timestamp of SphinxTrain will also be published. Recent Progress Better on-line help Added support for adaptation Better support in perl scripts for FCHMM (Evandro) Silence deletion in Baum-Welch Training (experimental)

Hieroglyph: Using Sphinx for building speech recognizers Project Hieroglyphs An effort to build a set of complete documentation for using Sphinx, SphinxTrain and CMU LM Toolkit fo building speech applications. Largely based on Evandro, Rita, Ravi, Roni’s docs. “Editor”: Arthur Chan <- do a lot of editing Authors: Arthur, David, Evandro, Rita, Ravi, Roni, Yitao

Hieroglyph: An outline Chapter 1: Licensing of Sphinx, SphinxTrain and LM Toolkit Chapter 2: Introduction to Sphinx Chapter 3: Introduction to Speech Recognition Chapter 4: Recipe of Building Speech Application using Sphinx Chapter 5: Different Software Toolkits of Sphinx Chapter 6: Acoustic Model Training Chapter 7: Language Model Training Chapter 8: Search Structure and Speed-up of the Speech recognizer Chapter 9: Speaker Adaptation Chapter 10: Research using Sphinx Chapter 11: Development using Sphinx Appendix A: Command Line Information Appendix B: FAQ

Hieroglyph: Status Still in the drafting stage Chapter I : License and use of Sphinx, SphinxTrain and CMU LM Toolkit (1 st draft, 3 rd Rev) Chapter II : Introduction to Sphinx, SphinxTrain and CMU LM Toolkit (1 st draft, 1 st Rev) Chapter VIII : Search Structure and Speed-up of Sphinx's recognizers (1 st draft, 1 st Rev) Chapter IX: Speaker adaptation using Sphinx (1 st draft, 2 nd Rev) Chapter XI: Development using Sphinx (1 st draft, 1 st Rev) Appendix A.2: Full SphinxTrain Command Line Information (1 st draft, 2 nd Rev) Writing Quality : Low The 1 st draft will be completed ½ year later (hopefully)

Team and Organization “Sphinx Developers”: A group of volunteers who maintain and enhance Sphinx and related resources Current Members: Arthur Chan (Project Manager / Coordinator) Evandro Gouvea (Maintainer / Developer) David Huggins-Daines (Developer) Yitao Sun (Developer) Ravi Mosur (Speech Advisor) Alex Rudnicky (Speech Advisor) All of you Application Developers Modeling experts Linguists Users

Team and Organization We need help! Several positions are still available for volunteers: Project Manager : Enable Development of Sphinx Translation: kick/fix miscellaneous people (lightly) everyday. Maintainer : Ensure integrity of Sphinx code and resource Translation: a good chance for you to understand life more Tester : Enable test-based development in Sphinx Translation: a good way to increase blood pressure. Developers : Incorporate state-of-art technology into Sphinx Translation: deal with legacy code and start to write legacy code yourself For your projects, you can also send us temp people. Regular meetings are scheduled biweekly. Though, if we are too busy, we just skip it.

Next 6 months: Sphinx 3.6 More refined speaker adaptation More support on dynamic LM More speed-up of the code Better documentation (Complete 1 st Draft of Hieroglyph?) Confidence measure(?)

If we still survive and have a full team…… Roadmap of Sphinx 3.X (X>6) X=7, Decoder, Trainer code merge FSG implementation Confidence annotation X=8 : Trainer fixes LM manipulation support X=9 : Better covariance modeling and speaker adaptation Hieroglyph completed X>= 10 : To move on, innovation is necessary.

Speech recognition and other Research The goal of Sphinx Support innovation and development of new speech applications A conscious and correct decision in long term speech recognition research In Speech Synthesis: aligner is important for unit selection In Parsing/Dialog Modeling: Sphinx 3.X still has a lot of errors! We still need Phoenix! (Robust Parser) We still need Ravenclaw House! (Dialog Manager) In Speech Applications Good recognizer is the basis

Cost of Research in Speech Recognition 30% WER reduction is usually perceivable to users i.e. roughly translate to 1-2 good algorithmic improvements Under a well-educated researchers group known techniques usually require ½ year to implement and test. Unknown techniques will take more time. (1 year per innovation) Experienced developers : 1 month to implement known techniques 3 months to innovate

Therefore…… It still makes sense to continuously support on, speech recognizer development acoustic modeling improvement. To consolidate, what we were lacking 1, code and project management Multi-developer environment is strictly essential. 2, transferal of research to development 3, acoustic modeling research: discriminative training, speaker adaptation

Future of Sphinx 3.X ICSLP 2004 “From Decoding Driven to Detection-Based Paradigms for Automatic Speech Recognition” by Prof. Chin-Hui Lee Speech Recognition: Still an open problem at 2004 Role of Speech Recognition in Speech Application: Still largely unknown Require open minds to understand

Conclusion We’ve done something in 2004 Our effort starts to make a difference We still need to do more in 2005 Making a Sphinx 3.X a backbone of speech application development Consolidation of the current research and development in Sphinx Seek for ways for sustainable development

Thank you!