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Grapheme-to-Phoneme for

ThaiPongthai Tarsaku

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ContentIntrodu

ctionGrapheme-to-Phoneme in TTS systemProblems in Thai

PGLR ApproachExperiment & Results & DiscussionConclusion

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IntroductionGrapheme-to-Phoneme

(G2P) is a module in TTS system.Grapheme-to-Phoneme approaches.Dictionary

base.Rule base.Statistical base.Probabilistic Generalized LR

(PGLR) parser is statistical base approach.

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G2P in TTS system

T e x t S e g m e n ta tio n

G ra p h e m e -to -P h o n e m e

P ro so d y G e n e ra tio n

S p e e c h S ig n a l S y n th e s is

ผ ม ข อ ข อ บ คุ� ณ ทุ� ก ทุ� า น ทุ�� ม า เยี่�� ยี่ ม ช ม ง า น

/ / / / / / / ผ ม ข อ ข อ บ คุ� ณ ทุ� ก ทุ� า น ทุ�� ม า เยี่�� ยี่ ม ช ม ง า น

/phom 4/k h@ :4/k h@ :p1/k hun0/thuk 3/tha:n2/thi :2/m a:0/j i :am 2/chom 0/nga:n0/

S p e e c h W a v e fo rm

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Problems in Thai (1)

“มณฑ ” า is pronounced as /mon0/tha:0/ “มณฑป” is pronounced as /mon0/dop1/“ ” เพลา (axe) is pronounced as /phlaw0/“ ” เพลา (time) is pronounced as /phe:0/la:0/

“ ” น��า is phonologically pronounced as /nam3/ but usually pronounced as /na:m3/

Ambiguity in grapheme-phoneme mapping.

Homograph.

Vowel’s length

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Problems in Thai (2)

“วิ�ทุ” in “วิ�ทุ ” ยี่า is pronounced as /wit2/tha2/

“อ�ฐิ�” is pronounced as /?at1/thi1/

“ ” ตากลม can be segmented into “ตา| ” กลม (round eye) and “ตาก| ” ลม (to expose wind) which are pronounced /ta:0/klom0/ and /ta:k1/lom0/ respectively.

Linking syllable pronunciation.Ambiguity in consonantal functionality..Word boundary.

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PGLR ApproachPGLR : Probabilistic

Generalize LR parsing.PGLR has advantage in context-sensitivity.PGLR is able to capture two levels of context.Global context - over structures

from the CFG rules.Local n-gram context.

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Context-Free Grammar Rules

A CFG rule is prepared for Thai syllable construction.A set of CFG rules is grouped by Thai vowel unit.( 21 groups and 3 special groups)CFG rules are able to cover both monosyllable and polysyllable.

<G r p_ 1>

<G r p_ 2><G r p_ 1>

<G r p_ 2>

<in it> า<in it> า <fi nal>เ <in it> เ <in it> <fi nal>

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PGLR parserPGLR parser

Thai Grapheme-to Phoneme system

Most probableparse tree

Most probableparse tree G-P MappingG-P Mapping Toneme

Generation

TonemeGeneration

PGLRTable

PGLRTable

CFG RulesCFG Rules G-P TableG-P Table

W

S y l

S y l S y l

ส มช า ยี่S y lS y l

p = 0 .3

W

S y l

S y l S y l

ส ม ช า ยี่

p = 0 .7

/som/chaj/ /som4/chaj0/

W

S y l

S y l S y l

ส ม ช า ยี่

p = 0 .7

สมชาย

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Grapheme-Phoneme Mapping

Example.W

S y lty p eA

ก า รk a: n

S y lty p eB

W

S y lty p eC

เ ษช ฐิ าch e: t th a:

S y lty p eD

W

S y lty p eE

ส ม พ รs m ph no @ :

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Experiment Database

LEXiTRON : The Thai electronic dictio nary is used for training and testing.

~23000 Thai words with pronunciation. TrainingFour-fifth of database is used for training. TestingOne-fifth of database is used for testing. Testing against the -rule based [Wiboon, 1999] and the decision tr

-ee based[Chotimongkol, 2000] systems.

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Result

Conversion (word) accuracy(%)Model

Exact match Ignorance ofVow. Length

PGLR 72.87 90.44

Rule-based 67.14 83.81

Decision Tree 68.76 86.94

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Discussion

Vowel’s length problem is dominant (90.44 -> 72.87).Half of all errors (~5%) come from linking syllable problem.To improve accuracy, more training data is required.

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Conclusion PGLR approach has

advantage in context-sensitivity (both global and local context). The efficiency of PGLR parser depends on carefully writing in CFG rules.

This approach can be applie d in syllable segmentation f

ramework or soundex conv ersion framework.

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Thank you

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Tone in Thai There are 5 tone levels

(Tonemes) in Thai.mid-level : 0 low-level : 1 falling-level : 2 high-level : 3 rising-level : 4

Toneme is depended on con sonant class, syllable type a

nd tone marker.

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Tonemic Gen erationTone Markers and Tonemes

ConsonantClass

Syllabletype

unmarked –่ –่ –่ � –่ �Live Syllable 4 1 2 3 4High

ClassDead Syllable 1 1 2 3 4

Live Syllable 0 1 2 3 4MiddleClass

Dead Syllable 1 1 2 3 4

Live Syllable 0 2 3 3 4

Dead ShortSyllable

3 2 2 3 4LowClass

Dead LongSyllable

2 1 3 3 4

High Class ขฃฉฐถผฝศษสหMiddle Class ก จฎฏดตบปอLow Class ค ฅฆงชซฌญฑฒณทธนพฟภมยรลวฬฮ

Dead SyllableLive Syllable Dead Short Syllable Dead Long Syllable

- the final consonantis n, ng, m, or j.

- long vowel with nofinal consonant (z).

- short vowel withfinal consonant k, t,or p.

- short vowel with nofinal consonant (z).

- long vowel withfinal consonant k, t,or p.

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GLR parserGLR parser parse tree[i]parse tree[i] G-P MappingG-P Mapping TonemeGeneration

TonemeGeneration

GLRTable

GLRTable

CFG RulesCFG Rules G-P TableG-P Table

W

S y l

S y l S y l

ส มช า ยี่S y lS y l

W

S y l

S y l S y l

ส ม ช า ยี่

W

S y l

S y l S y l

ส ม ช า ยี่

สมชาย

G-P TableG-P Table

Phoneme Comparison

Phoneme Comparison

The selected parse tree

is used for training

Increasing iIncreasing i

mismatch

match

Parse Tree Selection