Adaptive Statistical Utterance Phonetization for French

International audienceTraditional utterance phonetization methods concatenate pronunciations of uncontextualized constituent words. This approach is too weak for some languages, like French, where transitions between words imply pronunciation modifications. Moreover, it makes it difficult to consider global pronunciation strategies, for instance to model a specific speaker or a specific accent. To overcome these problems, this paper presents a new original phonetization approach for French to generate pronunciation variants of utterances. This approach offers a statistical and highly adaptive framework by relying on conditional random fields and weighted finite state transducers. The approach is evaluated on a corpus of isolated words and a corpus of spoken utterances

A Weighted Finite State Transducer tutorial

The concepts of WFSTs are summarised, including structural and stochastic optimisations. A typical composition process for ASR is described. Some experiments show that care should be taken with silence models

Acoustic Data-driven Pronunciation Lexicon for Large Vocabulary Speech Recognition

Speech recognition systems normally use handcrafted pronunciation lexicons designed by linguistic experts. Building and maintaining such a lexicon is expensive and time consuming. This paper concerns automatically learning a pronunciation lexicon for speech recognition. We assume the availability of a small seed lexicon and then learn the pronunciations of new words directly from speech that is transcribed at word-level. We present two implementations for refining the putative pronunciations of new words based on acoustic evidence. The first one is an expectation maximization (EM) algorithm based on weighted finite state transducers (WFSTs) and the other is its Viterbi approximation. We carried out experiments on the Switchboard corpus of conversational telephone speech. The expert lexicon has a size of more than 30,000 words, from which we randomly selected 5,000 words to form the seed lexicon. By using the proposed lexicon learning method, we have significantly improved the accuracy compared with a lexicon learned using a grapheme-tophoneme transformation, and have obtained a word error rate that approaches that achieved using a fully handcrafted lexicon. Index Terms — Lexical modelling, Probabilistic pronunciation model, Automatic speech recognition

Juicer: A Weighted Finite-State Transducer speech decoder

A major component in the development of any speech recognition system is the decoder. As task complexities and, consequently, system complexities have continued to increase the decoding problem has become an increasingly significant component in the overall speech recognition system development effort, with efficient decoder design contributing to significantly improve the trade-off between decoding time and search errors. In this paper we present the ``Juicer'' (from trans\textbf{\emph{ducer}}) large vocabulary continuous speech recognition (LVCSR) decoder based on weighted finite-State transducer (WFST). We begin with a discussion of the need for open source, state-of-the-art decoding software in LVCSR research and how this lead to the development of Juicer, followed by a brief overview of decoding techniques and major issues in decoder design. We present Juicer and its major features, emphasising its potential not only as a critical component in the development of LVCSR systems, but also as an important research tool in itself, being based around the flexible WFST paradigm. We also provide results of benchmarking tests that have been carried out to date, demonstrating that in many respects Juicer, while still in its early development, is already achieving state-of-the-art. These benchmarking tests serve to not only demonstrate the utility of Juicer in its present state, but are also being used to guide future development, hence, we conclude with a brief discussion of some of the extensions that are currently under way or being considered for Juicer

A SYSTEM FOR AUTOMATIC ALIGNMENT OF BROADCAST MEDIA CAPTIONS USING WEIGHTED FINITE-STATE TRANSDUCERS

ABSTRACT We describe our system for alignment of broadcast media captions in the 2015 MGB Challenge. A precise time alignment of previously-generated subtitles to media data is important in the process of caption generation by broadcasters. However, this task is challenging due to the highly diverse, often noisy content of the audio, and because the subtitles are frequently not a verbatim representation of the actual words spoken. Our system employs a two-pass approach with appropriately constrained weighted finite state transducers (WFSTs) to enable good alignment even when the audio quality would be challenging for conventional ASR. The system achieves an f-score of 0.8965 on the MGB Challenge development set

Neural Network vs. Rule-Based G2P: A Hybrid Approach to Stress Prediction and Related Vowel Reduction in Bulgarian

An effective grapheme-to-phoneme (G2P) conversion system is a critical element of speech synthesis. Rule-based systems were an early method for G2P conversion. In recent years, machine learning tools have been shown to outperform rule-based approaches in G2P tasks. We investigate neural network sequence-to-sequence modeling for the prediction of syllable stress and resulting vowel reductions in the Bulgarian language. We then develop a hybrid G2P approach which combines manually written grapheme-to-phoneme mapping rules with neural network-enabled syllable stress predictions by inserting stress markers in the predicted stress position of the transcription produced by the rule-based finite-state transducer. Finally, we apply vowel reduction rules in relation to the position of the stress marker to yield the predicted phonetic transcription of the source Bulgarian word written in Cyrillic graphemes. We compare word error rates between the neural network sequence-to-sequence modeling approach with the hybrid approach and find no significant difference between the two. We conclude that our hybrid approach to syllable stress, vowel reduction, and transcription performs as well as the exclusively machine learning powered approach