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Applying the Pronunciation Lexicon Specification to ASR & TTS

1. Applying the Pronunciation Lexicon Specification to ASR & TTS. Patrizio Bergallo. SpeechTEK ASTS - Advances in Text-to-Speech Processing. Monday , August 20, 2007. Agenda. Loquendo Today Introduction to PLS Reference Scenario Pronunciation Lexicons International Phonetic Alphabet

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Applying the Pronunciation Lexicon Specification to ASR & TTS

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  1. 1 Applying the Pronunciation Lexicon Specification to ASR & TTS Patrizio Bergallo SpeechTEK ASTS - Advances in Text-to-Speech Processing Monday, August 20, 2007

  2. Agenda • Loquendo Today • Introduction to PLS • Reference Scenario • Pronunciation Lexicons • International Phonetic Alphabet • Overview of PLS • How does TTS use PLS? • How does ASR use PLS? • Examples of Use • Latest Improvements

  3. Loquendo Today • Global company of the Telecom Italia group, leader in Europe and South America in the Speech Technologies market • Company founded in 2001 from Telecom Italia Labs, benefiting from know-how gained from more than 30 years research experience • Complete set of Multilingual speech technologies on a wide spectrum of devices; 25 patents, 50 voices and 20 languages • Full support for international standards (MRCPv1/v2, VoiceXML 2.0/2.1, CCXML, SSML, SRGS, SISR) • Company ready for challenging future scenarios: Multimodality, Security • 100 employees, and displayed strong growth throughout 2007 • HQ in Turin, Offices in US, Spain, Germany and France, and a Worldwide Network of Partners

  4. Reference Scenario • Many speech applications need to specify pronunciation for words and phrases • Surnames, locations, company names • Acronyms • Names in specific contexts (restaurants, sports, movie titles, etc.) • Foreign words, mixed languages • Pronunciation is critical both for TTS and ASR • Improves reading of prompts by TTS • Improves ASR performance • VoiceXML 2.0/2.1 applications are the reference scenario • Prompts are based on SSML 1.0 (or in future SSML 1.1) • Recognition grammars are based on SRGS 1.0

  5. Pronunciation Lexicons • Pronunciation Lexicon • a mapping between words (or short phrases), their written representations, and their pronunciations suitable for use by an ASR engine or a TTS engine • Pronunciation lexicons are not only useful for voice browsers • They have also proven effective mechanisms to support accessibility for the differently able as well as greater usability for all users • They are used to good effect in screen readers and user agents supporting multimodal interfaces • The W3C Pronunciation Lexicon Specification (PLS) Version 1.0 is designed to enable interoperable specification of pronunciation lexicons

  6. Pronunciation Lexicon Specification • W3C specification status • Second Last Call Working Draft (26 October, 2006) • Currently the Implementation Report Plan and the Disposition of Comments are under development (all public comments were addressed) • Candidate Recommendation expected 3Q07 Part of first version of the Speech Interface Framework (Larson, 2000) W3C Recommendation W3C Last Call Working Draft

  7. International Phonetic Alphabet • Pronunciation is represented by a phonetic alphabet • Standard phonetic alphabets • International Phonetic Alphabet (IPA) • Well known phonetic alphabet • SAMPA - ASCII based (simple to write) • Pinyin (Chinese Mandarin), JEITA (Japanese), etc. • Proprietary phonetic alphabets • International Phonetic Alphabet (IPA) • Created by International Phonetic Association (active since 1896), collaborative effort by all the major phoneticians around the world • Universally agreed system of notation for sounds of languages • Covers all languages • Requires UNICODE to write it • Normatively referenced by PLS

  8. Overview of PLS • A PLS document is a container (<lexicon>) of several lexical entries (<lexeme>) • Each lexical entry contains • One or more spellings (<grapheme>) • One or more pronunciations (<phoneme>) or substitutions (<alias>) • Each PLS document is related to a single unique language (xml:lang) • SSML 1.0 and SRGS 1.0 documents can reference one or more PLS documents • Current version doesn’t include morphological, syntactic and semantic information associated with pronunciations

  9. PLS Example <?xml version="1.0" encoding="UTF-8"?> <lexicon version="1.0" xmlns="http://www.w3.org/2005/01/pronunciation-lexicon" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3.org/2005/01/pronunciationlexicon http://www.w3.org/TR/2007/CR-pronunciation-lexicon2007@@@@/pls.xsd" alphabet="ipa" xml:lang="en-US"> <lexeme> <grapheme>Sepulveda</grapheme> <phoneme>səˈpʌlvɪdə</phoneme> </lexeme> <lexeme> <grapheme>W3C</grapheme> <alias>World Wide Web Consortium</alias> </lexeme> </lexicon>

  10. How does TTS use PLS? • SSML 1.0 <?xml version="1.0" encoding="UTF-8"?> <speak version="1.0" … xml:lang="en-US"> <lexicon uri="http://www.example.com/SSMLexample.pls"/> The title of the movie is: "La vita è bella" (Life is beautiful), which is directed by Benigni. </speak> • PLS 1.0 <?xml version="1.0" encoding="UTF-8"?> <lexicon version="1.0" … alphabet="ipa" xml:lang="en-US"> <lexeme> <grapheme>La vita è bella</grapheme> <phoneme>ˈlɑ ˈviːɾə ˈʔeɪ ˈbɛlə</phoneme> </lexeme> <lexeme> <grapheme>Benigni</grapheme> <phoneme>bɛˈniːnji</phoneme> </lexeme> </lexicon>

  11. How does ASR use PLS? • SRGS 1.0 <?xml version="1.0" encoding="UTF-8"?> <grammar version="1.0" … xml:lang="en-US” root="movies" mode="voice"> <lexicon uri="http://www.example.com/SRGSexample.pls"/> <rule id="movies" scope="public"> <one-of> <item>Terminator 2: Judgment Day</item> <item>Pluto's Judgement Day</item> </one-of> </rule> </grammar> • PLS 1.0 <?xml version="1.0" encoding="UTF-8"?> <lexicon version="1.0" … alphabet="ipa" xml:lang="en-US"> <lexeme> <grapheme>judgment</grapheme> <grapheme>judgement</grapheme> <phoneme>ˈdʒʌdʒ.mənt</phoneme> </lexeme> </lexicon>

  12. Examples of Use • Multiple pronunciations for the same orthography • Multiple orthographies • Homophones • Homographs • Acronyms, Abbreviations, etc.

  13. Multiple pronunciations for the same orthography • Multiple pronunciations are represented by more than one <phoneme> or <alias> element <?xml version="1.0" encoding="UTF-8"?> <lexicon version="1.0" … alphabet="ipa" xml:lang="en-GB"> <lexeme> <grapheme>Newton</grapheme> <phoneme>ˈnjuːtən</phoneme> <phoneme>ˈnuːtən</phoneme> </lexeme> </lexicon>

  14. Multiple orthographies • Alternative textual representations for the same word or phrase are represented by more than one <grapheme> inside the same <lexeme> • All the pronunciations given within the <lexeme> apply to each and every <grapheme> within the <lexeme> <?xml version="1.0" encoding="UTF-8"?> <lexicon version="1.0" … alphabet="ipa" xml:lang="jp"> <lexeme> <grapheme>nihongo</grapheme> <grapheme>日本語</grapheme> <grapheme>にほんご</grapheme> <phoneme>ɲihoŋo</phoneme> </lexeme> </lexicon>

  15. Homophones • Words with the same pronunciation but different meanings are represented as different lexemes <?xml version="1.0" encoding="UTF-8"?> <lexicon version="1.0" … alphabet="ipa" xml:lang="en-US"> <lexeme> <grapheme>cede</grapheme> <phoneme>siːd</phoneme> </lexeme> <lexeme> <grapheme>seed</grapheme> <phoneme>siːd</phoneme> </lexeme> </lexicon>

  16. Homographs (1/2) • Words with the same spelling but pronounced in different ways are represented using the role attribute of the <lexeme> element • This mechanism allows for the referencing of defined taxonomies of word classes (part of speech, meaning, etc.) <lexicon version="1.0“ xmlns:claws=“http://www.example.com/claws7tags” alphabet="x-myorganization-pinyin" xml:lang="zh-CN"> <lexeme role="claws:VV0"> <!-- base form of lexical verb --> <grapheme>处</grapheme> <phoneme>chu3</phoneme> <!-- pinyin string is: "chǔ" in 处罚 处置 --> </lexeme> <lexeme role="claws:NN"> <!-- common noun, neutral for number --> <grapheme>处</grapheme> <phoneme>chu4</phoneme> <!-- pinyin string is: "chù" in 处所 妙处 --> </lexeme> </lexicon>

  17. Homographs (2/2) • SSML 1.1 will support the role attribute <speak version="1.1“ xmlns:claws="http://www.example.com/claws7tags" xml:lang="zh-CN"> <lexicon uri="http://www.example.com/lexicon.pls“ type="application/pls+xml“ xml:id="mylex"/> <lookup ref="mylex"> 他这个人很不好相<w role="claws:VV0">处</w>。 此<w role="claws:NN">处</w>不准照相。 </lookup> </speak> • Currently PLS doesn’t define/mandate any taxonomy • PLS generally defines role values as qualified names (QNames)

  18. Acronyms, Abbreviations, etc. • Pronunciations expressed as a sequence of other orthographies (acronyms, abbreviations, etc.) are represented by the <alias> element <?xml version="1.0" encoding="UTF-8"?> <lexicon version="1.0" … alphabet="ipa" xml:lang="en-US"> <lexeme> <grapheme>W3C</grapheme> <alias>World Wide Web Consortium</alias> </lexeme> <lexeme> <grapheme>101</grapheme> <alias>one hundred and one</alias> </lexeme> </lexicon>

  19. Latest Improvements • W3C Last Call Working Draft stage allows public comments to be addressed • Large majority were clarifications • New functionalities were deferred to a future version of PLS specification • Major clarifications were about • <alias> recursion • Multiple pronunciations • Changes are subject to a formal approval by the Working Group • Next Steps • PLS 1.0 is very close to Candidate Recommendation stage • SSML 1.1 will provide a more complete support of PLS 1.0

  20. <alias> recursion • Pronunciations of the <alias> element contents MUST be generated by the processor, using pronunciations described by the <phoneme> element of any constituent graphemes in the PLS document, and without invoking recursive access to the PLS document on the <alias> elements of any constituent graphemes <?xml version="1.0" encoding="UTF-8"?> <lexicon version="1.0" … alphabet="ipa" xml:lang="en-US"> <lexeme> <grapheme>GNU</grapheme> <alias>GNU is Not Unix</alias> <phoneme>gəˈnuː</phoneme> </lexeme> <lexeme> <grapheme>Unix</grapheme> <grapheme>UNIX</grapheme> <alias>a multiplexed information and computing service</alias> <phoneme>ˈjuːnɪks</phoneme> </lexeme> </lexicon> GNU is pronounced: gəˈnuː is Not ˈjuːnɪks

  21. Multiple pronunciations (1/2) • ASR • If more than one pronunciation for a given <lexeme> is specified, an ASR processor MUST consider each of them as valid pronunciations for the <grapheme> • TTS • If more than one pronunciation for a given <lexeme> is specified, a TTS processor MUST use the first one in document order that has the prefer attribute set to "true“ • If none of the pronunciations has prefer set to "true", the TTS processor MUST use the first one in document order unless theTTS processor is documented as having a method of selecting pronunciations, in which case the processor MUST use any one of the pronunciations

  22. Multiple pronunciations (2/2) • An ASR processor will recognize both pronunciations, whereas a TTS processor will only use the first one (because it is the first in document order that has prefer set to "true"). <?xml version="1.0" encoding="UTF-8"?> <lexicon version="1.0" … alphabet="ipa" xml:lang="en-US"> <lexeme> <grapheme>lead</grapheme> <alias prefer="true">led</alias> <phoneme prefer="true">liːd</phoneme> </lexeme> <lexeme> <grapheme>led</grapheme> <phoneme>led</phoneme> </lexeme> </lexicon>

  23. References • PLS 1.0 Second Last Call Working Draft (26 October, 2006) • http://www.w3.org/TR/2006/WD-pronunciation-lexicon-20061026/ • Voice Browser Activity Page (VoiceXML, SSML, SRGS, …) • http://www.w3.org/Voice/ • International Phonetic Association • http://www.arts.gla.ac.uk/IPA/ • VoiceXML Forum • http://www.voicexml.org/

  24. Final Remarks • For more information please • Visit Loquendo’s booth#509 • Keep an eye on: www.loquendo.com • Contact us: patrizio.bergallo@loquendo.com THANK YOU

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