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prontron - PRONunciation percepTRON
    by Graham Neubig

prontron is a tool for pronunciation estimation, mainly focusing on the pronunciation of Japanese unknown words, but written in a general way so it can be used for any string-to-string conversion task. I created it as a quick challenge to see if I could apply discriminative learning (the structured perceptron) to Japanese pronunciation estimation, but I am posting it in case anybody will find it useful.

--- Download/Install ---

Download the latest version from

The code of prontron is distributed according to the Common Public License v 1.0, and can be distributed freely according to this license.

--- Estimating Pronunciations with prontron ---

To estimate the pronunciation of words with prontron, you can use the models included in the model directory. If you have a file input.txt with one word per line, run the program as follows:

$ model/model.dict model/model.feat < input.txt > output.txt

This will output pronunciations, one per line, into output.txt.

--- Training prontron ---

Prontron training is a two step process. First, you have to build a dictionary of "subword/pronunciation" pairs, then run weight training.

First, create two files train.word and train.pron that contain words and their pronunciations. Then run the alignment program to create a dictionary model/model.dict of subword/pronunciation pairs:

$ train.word train.pron model/model.dict

You can add more entries to the dictionary if you notice that anything important is missing. Next, we train the feature weights model/model.feat using the perceptron algorithm.

$ train.word train.pron model/model.dict model/model.feat

That is it! Both of these programs have a number of training options (mins and maxes should be the same for

    -fmin  minimum length of the input unit (1)
    -fmax  maximum length of the input unit (1)
    -emin  minimum length of the output unit (0)
    -emax  maximum length of the output unit (5)
    -iters maximum number of iterations (10)
    -word  use word units instead of characters only:
    -cut   all pairs that have a maximum posterior probability 
           less than this will be trimmed (0.001) only:
    -inarow  skip training examples we've gotten right
             this many times
    -recheck re-check skipped examples in this many times 

--- How Does it Work? ---

Prontron uses discriminative training based on the structured perceptron. This is good, because it lets the training many arbitrary features. The basic idea of the structured perceptron algorithm is:

    * Given a set of feature weights h, for a certain word w find the highest scoring pronunciation p, and its set of features f(p).
    * If p is not equal to the correct pronunciation p*, reduce the weights for features f(p) and increase weights of features of f(p*).
    * Repeat this for every word in the corpus many times until we find good weights.

In the case of pronunciation estimation, it is not too difficult to find p, f(p), and f(p*) using the Viterbi algorithm. For the current features in prontron, we use bigram and length features over four sequences:

Word:	発音 	発表
Pronunciation:	はつおん 	はっぴょう
Seq1 -- Char/Pron. Pairs:	発/はつ 音/おん	発/はっ 表/ぴょう
Seq2 -- Pron. Strings:	はつ おん	はっ ぴょう
Seq3 -- Pron. Characters:	は つ お ん	は っ ぴ ょ う
Seq4 -- (Almost) Phonemes:	h a t u o n	h a x p i xyo u

Examples of the features learned over each of these sequences are as follows:

--- Contributors ---

    * Graham Neubig (main developer)

If you are interested in participating in the prontron project, particularly tackling any of the interesting challenges below, please send an email to neubig at gmail dot com.

--- TODO List ---

There are a bunch of possible improvements that would be quite interesting and useful:

    * Regularization: Currently the perceptron is unregularized, but adding L1 or L2 regularization could reduce the number of features and increase performance.
    * N-best Decoding: Currently prontron can only give one-best answers.
    * Large-Margin Traning: Large-margin techniques such as support vector machines can be learned online. They are simple to implement, but require at least 2-best decoding.
    * Other Loss Functions: Prontron currently only supports one-zero loss (examples are right, or not), but it would probably be better to do loss based on mora error rate. This is not, however, trivial to do.

--- Revision History ---

Version 0.1.0 (7/10/2011)

    * Initial release!


A discriminative pronunciation estimator using the structured perceptron algorithm.



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