Progress of Sphinx 3.X From X=5 to X=6 Arthur Chan Evandro Gouvea David J. Huggins-Daines Alex I. Rudnicky Mosur Ravishankar Yitao Sun

If you want to leave now…… Take home message 1 Sphinx 3.6 Rocks!

Here is another one…… Take home message 2 We need Better Acoustic Models We need Better Acoustic Models.

This talk (~37 pages) Overview (6 pages) Better Software Architecture (9 pages) Speed of Sphinx 3.6 (3 pages) Accuracy Improvement (7 pages) Functionalities Improvement (3 pages) Documentation (4 pages) Sphinx 3.X (X>6) and Conclusion (~5 pages) Discussion (10 mins?)

Overview of CMU Sphinx

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

Family of CMU Sphinx Decoders Sphinx {II – IV} PocketSphinx (by Dave at Oct 2005) Acoustic Model Trainer SphinxTrain Documentation Hieroglyphs Robust/SphinxTrain Tutorial

Sphinx Developers Sphinx is maintained by Volunteer programmers/researchers who like speech recognition Funded by different projects Motivated by different reasons All contribution go to the same codebase Goal : Sustainable development of Sphinx Sphinx Developer Meetings are held regularly secretly to decide the way to go in Sphinx

What is Sphinx 3.X? An extension of Sphinx 3’s recognizers “Sphinx 3.X (X=6)” means “Sphinx 3.6” Provide more functionalities such as Real-time speech recognition Speaker adaptation Developers Application Interfaces (APIs) Different search algorithms 3.X (X>3) is motivated by Project CALO and GALE

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 -live-mode demo S3.4 -fast GMM, class- based LM, dynamic LM S3.5 –some support on speaker adaptation -live mode APIs 3.X/3.0 merge - Better Search Architecture/Implementation -More support for Speaker Adaptation - Gentle Re-factoring of code-base -Somme support on FSG decoding and confidence -Better Documentation/Tutorial lm_convert (lm3g2dmp) dp 3.6

This talk – Progress of Sphinx 3.6 From the perspective of a developer an observer Sphinx 3.6 Where are we now? Where will we go? Summary of 5 talks

Software Architecture of Sphinx 3.X (X=6)

Motivation of Re-Architecting Sphinx 3.X We start to need a new search algorithms New search algorithm development could have risk. We don’t want to throw away the old one. Mere replacement could cause backward compatibility problem. Code has grown to a stage where Some changes could be very hard. Multiple programmers become active at the same time CVS conflict could become often if things are controlled by “if-else” structure

Architecture of Sphinx 3.X (X<6) Batch sequential Architecture (Shaw 96) Each executable has customized sub- routines decode livepretend Decode_anytopo align allphone GMM Computation 1 approx_cont_mgau Search 1 Process Controller 1 GMM Computation 2 (Using gauden & senone Method 1) Search 2 Process Controller 2 GMM Computation 3 (Using gauden & senone Method 2) Search 3 Process Controller 3 GMM Computation 4 (Using gauden & senone Method 3) Search 4 Process Controller 4 Command Line 1Command Line 2Command Line 3Command Line 4 Initialization 1 (kb and kbcore) Initialization 2Initialization 3Initialization 4

Architecture Diagram of Sphinx 3.6 Applications Controllers/ Abstractions ImplementationsLibraries decode livepretend align allphone dag astar livedecode API Search Controller Process Controller Search Initializer Command Line Processor User Defined Applications Fast Single Stream GMM Computation Multi Stream GMM Computation FSG Search Flat Lexicon Search Dictionary Library Search Library LM Library AM Library Utility Library Feature Library Miscellaneous Library decode (anytopo) Tree Lexicon Search

Separation of Mechanism and Implementation Search Mechanism Module (srch.c) -A class provides Atomic Search Operations (ASOs) in the form of function pointers -Configured by just setting function pointers - A single interface for applications Search Implementation Module (srch.c) Search Implementation Module (srch.c) Search Implementation Module (srch.c) Search Implementation Module (srch.c) Search Implementation Modules (srch_????.c) -Could have many of them -Possibilities: A, Decoding with different implementations B, Concept of search including -alignment, -phoneme recognition -keyword spotting.

Search Mechanism Module – What does it do? Computation of One Frame Select Active CD Senone Compute Approx. GMM Score (CI senone) Compute Detail GMM Score (CD senone) Compute Detail HMM Score (CD) Propagate Graph (Phone- Level) Rescoring At word End using High-Level KS (e.g. LM) Propagate Graph (Word- Level) Search For One Frame GMM Compute

Search Implementations Implemented (-op_mode) Finite State Grammar Search (Mode 2) Flat Lexicon Search (Mode 3) Tree Search (Mode 4) Not in 3.6 Aligner (Mode 0) Phoneme recognition (Mode 1) A new tree search (Mode 5)

Different ways to implement search implementations 1, Use default implementation Just specify all atomic search operations (ASOs) provided 2, Override “search_one_frame” Only need to specify GMM computation and how to “search_one_frame” 3, Override the whole mechanism For people who dislike the default so much Override how to “search”

Consequence of Re-factoring Calling decode Could use flat-lexicon decoding as well decode_anytopo still exists For backward compatibility decode_anytopo = decode allphone, align, decode_anytopo could use fast GMM computation decode could use S3’s SCHMM Command-line is now synchronized

Summary on the Architecture Sphinx 3.6 A gentle re-factoring has carried out. A more flexible architecture A better playground for AM and search people S2 SCHMM computation routine? NN, SVM, ML techniques for AM?

Speed of Sphinx 3.6

Speed in Sphinx 3.6 Further work on Context-Independent Senone-based GMM Selection (CIGMMS) 20-30% Speed Up 3 tricks were proposed Fixed amount of CD senone compute. Use of best Gaussian index Tightening factor of CI-phone beam Published in “On Improvements of CI-based GMM Selection “ (Chan 2005)  but not very well received Alright, there are accuracy lost

A note on Sphinx 3.6 Speed Performance Sphinx 3.X works under 1xRT in most tasks. E.g. Smartnote/Sphinx Integration Broadcast News UNTUNED RESULT: 1.5xRT Sphinx 3.X is still slower than Sphinx 2 Fast setup of Sphinx 2: use 256 codeword SCHMM Fast setup of Sphinx 3: use senone FCHMM Historical notes: Comparable SCHMM setup has 4096 codewords Need benchmarking to truly judge

Speed - Conclusion Sphinx 3.X is in a reasonable level Sphinx 2 should still be used in speed- critical condition Further work GALE/CALO will still be around in 3.6/3.7 Accuracy become more motivated than speed

Accuracy Improvement During Sphinx 3.6

Our Immediate Problem What help us more in accuracy? Acoustic modeling ? Speaker Adaptation ? Search Improvement ?

Accuracy Improvement of Sphinx 3.6 – Speaker Adaptation Speaker adaptation techniques are shown to be crucia Even in tough task (e.g. CALO) 10-15% relative improvement Gain similar to LM/AM modeling work

Accuracy Improvement of Sphinx 3.6 – Speaker Adaptation (cont.) Dave has done a great job on Multiple-class MLLR MAP adaptation Things to watch Ziad’s VTLN implementation

Conclusion in Speaker Adaptation Observation in 3.6 Speaker adaptation is very important. What we still need: Maximum likelihood linear transformation (MLLT) Combination of MLLT, MLLR, MAP and VTLN Proved to be additive

Accuracy Improvement of Sphinx Search Our Attempts in Flat Lexicon Decoder Full triphones 2.5% rel. gain But 100xRT Full trigram Will give another 5-10 times slowdown Diff between Tree vs Flat Lex. Decoder 5% relative Conclusion: Further improvement in search is limited

Accuracy Improvement in Sphinx 3.6 -Modeling Mainly on addition of data (Major contributor) interpolation of LM (very decent gain) Things to watch: Yi’s LDA Yet to explore Speaker Adaptive Training (SAT) Semi-tied Covariance (STC) Matrix Conclusion: Commodity techniques are still not widely used in Sphinx (Bad sign).

Conclusion of Accuracy Improvement has a healthy development in speaker adaptation Improvement in search is hard Need 10x effort on acoustic modeling Commodity techniques are still not there Three final keywords: MLLT, SAT, STC Priorities: Adaptation > AM, LM > 2 stage Search >> 1 st Stage

Other Extensions in Sphinx 3.6

FSG search 3.6 supports FSG search Adapted from Sphinx 2’s implementation Current Issues No lextree implementation Static allocation of all HMMs; not allocated “on demand” FSG transitions represented by NxN matrix Other wish list No histogram pruning No state-based implementation Need more testing

Confidence Annotation conf Adapted from Rong with permission Compute Word Posterior Probability of a word given lattice Still under work

Language Model Related Now fully supports Text-based LM reading Inter-conversion of LM in TXT & DMP format lm_convert = lm3g2dmp++ LM switching API in live_decode_API

Documentation/Tutorial

Hieroglyphs A collection of documentation of using Sphinx 3, SphinxTrain and CMU LM Tool kit 1 st Draft is completed All chapter are filled with information. Writing the 2 nd Draft “Chief Editor”: Arthur Chan Does it even exist?

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

Book Reviews of Hieroglyphs “You wrote the worst preface I have ever seen in my life. “ Dr. Evandro Gouvea “The content is o. k., but the writing is still ……” Prof. Alex I. Rudnicky “Wow, it is thick. And, oh…… there are no blank spaces! You are not supposed to add contents in any CMU open source manuals, don’t you know?” Dr. Alan W. Black

Other Documents Robust Tutorial (Aka Sphinx 101) Thanks to Evandro Now could be used for archive_s3 Sphinx 2 Sphinx 3 Doxygen documentation for Sphinx 3.x is fully available xygen/html/ xygen/html/

Sphinx 3.X (X>6) and Conclusion

What is important? Keep the current design priorities: 1, Accuracy We are just OK and we badly need to improve it. 2, Speed We are OK and it doesn’t hurt to improve it 3, Functionalities Still a pain to use Sphinx 3 but it is constant improved Usability eventually implies distributing models. Accuracy should be prior to Speed No excuse in 3.7

Roadmap: In X=7…… For GALE/CALO Speaker Clustering/SAT Bridging SI and SA VTLN LDA 0.5 x CALO may need further speed improvement BBI More secret ideas in GMM computation

Roadmap (cont.) X=8 D.T. MMIE, MCE STC Interface with HTK model X=9 D.T. + S.A. X>10 Time to fire Arthur Chan and hire an assistant professor

Sphinx in Other Languages?

Other Possibilities of Sphinx? [You fill in this part]

We need your help! Project Manager: Enable Development of Sphinx Translation: Kick/Fix people and Kicked/Fixed by Evandro Developers: Incorporate state-of-art speech technology into Sphinx Translation: Fix 1 bug and Generate 5 more Maintainer: Ensure integrity of Sphinx code and resource Translation: You become so called the “Grand Janitor of Sphinx”. Tester: Enable test-based development in Sphinx Translation: You will learn a lot of Zen-Buddhism.

Our Current Motto (Subject to Change) “Don’t ever underestimate yourself…… You never know what a kind of mess you could make.” -Dr. Evandro Gouvea

Conclusion for Sphinx 3.X We have done something We are making some sense in the system development now We have healthy growth in accuracy But we still need more

Q & A

Thank you Acknowledgement Rich/Alan: for your constant encouragement Alex: for your understanding of Yin/Yang Rong: for contributing the confidence estimation program Bano: for reminding me I could die at any time when we were in Lake Arthur -> Hieroglyphs 1 st draft’s progress sped up. Sphinx developers: without you, I won’t be the “Grand Janitor”. Sphinx users: for your capabilities of giving me nightmares

Postscript, a word from my friend “Don’t ever underestimate yourself…… You never know what a mess you could make.” –Dr. Evandro Gouvea

Reserved

Pros/Cons of Batch Sequential Architecture Pros: Great flexibility for individual programmers No assumption, data structure are usually optimized for the application. Align and allphone have optimization. Crafting in individual application has high quality Cons: Great difficulty in maintenance Most changes need to be carried out for 5-6 times. Spread disease of code duplication Code with functionality was duplicated multiple times