Introduction of Grphones

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# Introduction of Grphones - PowerPoint PPT Presentation

Introduction of Grphones. Dong Wang 05/05/2008. Content. Grphones Graphone-based LVCSR Graphone-based STD. Graphones. Suppose graphemes and phonemes are two streams from a single stochastic process. Example speaking s p ea k i ng [spi:king] [s] [p] [i:] [k] [i] [ng].

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### Introduction of Grphones

Dong Wang

05/05/2008

Content
• Grphones
• Graphone-based LVCSR
• Graphone-based STD
Graphones
• Suppose graphemes and phonemes are two streams from a single stochastic process
• Example

speaking s p ea k i ng

[spi:king] [s] [p] [i:] [k] [i] [ng]

Graphones
• The grapheme-phoneme join units are called graphones.
• Suppose no context dependence among graphones, leading to simplest graphone model. With a known alignement L, the join probability can be written:
• The whole work is to define u and estimate p(u)
Graphones
• If the graphon model is ready, we can estimate the phoneme sequence from a grapheme sequence, and vice versa.

Deligne, Sabine / Yvon, Francois / Bimbot, Frédéric (1995): "Variable-length sequence matching for phonetic transcription using joint multigrams", In EUROSPEECH-1995, 2243-22

Graphones
• As the alignment is unkown in the training corpus (dictionary), an EM procedure can be used, with the alignment as latent variable.

Z

E

E

E

E

P

z

i

p

Graphones
• Iterative process is as the following, where c is the counts of occurrence:
• A forward-back process is used to avoid redundant computation
Graphones
• Some tricks
• Null grapheme or phoneme segment is allowed, however null-null graphones are not allowed
• Mutual information could be used to estimate the model accuracy among different length variables
• In English, I used gg length from 0-3, while pp length from 0-1.
Graphones
• Some experiments
• Mutual information:

gr(0-3)ph(0-1): 0.86 gr(0-1)ph(0-1): 0.58

• High-probable graphones

A+ax 7.587430e-01

E+iy 6.197528e-02

I+ay 4.753983e-02

O+ow 4.640152e-02

A+ 1.886822e-02

+ax 1.882734e-02

VE+v 1.074523e-02

ER+er 8.942506e-03

LL+l 8.298488e-03

CH+ch 5.454664e-03

SS+s 2.709674e-03

Graphone-based LVCSR
• M. Bisani, H. Ney , Multigram-based Grapheme-to-Phoneme Conversion for LVCSR , In Proc. Eurospeech, Geneva, Switzerland, 2003

Transcribe lexicon for new words using graphone models

Graphone-based STD
• Using multi-gram model to generate graphone forms for out-of-vocabulary words.
• Train hybrid language models which contains both in-vocabulary words and graphones.
• Decoding using the lexicon expanded with graphones.
• Searching INV words as in word lattices, and OOV words as in phoneme lattices.

Murat Akbacak, Dimitra Vergyri, Andreas Stolcke ,OPEN-VOCABULARY SPOKEN TERM DETECTION USING GRAPHONE-BASED HYBRID RECOGNITION SYSTEMS , ICASSP08, Los Angels, USA.

Graphone-based STD
• Only the hybrid system can detect OOV words
• For INV words, the hybrid system works better also.

Murat Akbacak, Dimitra Vergyri, Andreas Stolcke ,OPEN-VOCABULARY SPOKEN TERM DETECTION USING GRAPHONE-BASED HYBRID RECOGNITION SYSTEMS , ICASSP08, Los Angels, USA.

Graphone-based STD
• What is the difference between grahpone and phoneme based STD, considering OOV?
• How if we use decision trees to perform the LTS?
• How if we train the multi-gram using the whole text corpus, instead of the dictionary, hence including the frequency information?
Conclusions
• Graphone model is an alternative for decision trees to performance LTS.
• Graphone models can be used to detect multi-letter graphemes
• Word-subword hybrid system seems interesting.