Development of Indonesian Large Vocabulary Continuous Speech Recognition System within A-STAR Project

The paper outlines the development of a large vocabulary continuous speech recognition (LVCSR) system for the Indonesian language within the Asian speech translation (A-STAR) project. An overview of the A-STAR project and Indonesian language characteristics will be briefly described. We then focus on a discussion of the development of Indonesian LVCSR, including data resources issues, acoustic modeling, language modeling, the lexicon, and accuracy of recognition. There are three types of Indonesian data resources: daily news, telephone application, and BTEC tasks, which are used in this project. They are available in both text and speech forms. The Indonesian speech recognition engine was trained using the clean speech of both daily news and telephone application tasks. The optimum performance achieved on the BTEC task was 92.47% word accuracy. 1 A-STAR Project Overview The A-STAR project is an Asian consortium that is expected to advance the state-of-the-art in multilingual man-machine interfaces in the Asian region. This basic infrastructure will accelerate the development of large-scale spoken language corpora in Asia and also facilitate the development of related fundamental information communication technologies (ICT), such as multi-lingual speech translation, Figure 1: Outline of future speech-technology services connecting each area in the Asian region through network. multi-lingual speech transcription, and multi-lingual information retrieval. These fundamental technologies can be applied to the human-machine interfaces of various telecommunication devices and services connecting Asian countries through the network using standardized communication protocols as outlined in Fig. 1. They are expected to create digital opportunities, improve our digital capabilities, and eliminate the digital divide resulting from the differences in ICT levels in each area. The improvements to borderless communication in the Asian region are expected to result in many benefits in everyday life including tourism, business, education, and social security. The project was coordinated together by the Advanced Telecommunication Research (ATR) and the National Institute of Information and Communications Technology (NICT) Japan in cooperation with several research institutes in Asia, such as the National Laboratory of Pattern Recognition (NLPR) in China, the Electronics and Telecommunication Research Institute (ETRI) in Korea, the Agency for the Assessment and Application Technology (BPPT) in Indonesia, the National Electronics and Computer Technology Center (NECTEC) in Thailand, the Center for Development of Advanced Computing (CDAC) in India, the National Taiwan University (NTU) in Taiwan. Partners are still being sought for other languages in Asia. More details about the A-STAR project can be found in (Nakamura et al., 2007). 2 Indonesian Language Characteristic The Indonesian language, or so-called Bahasa Indonesia, is a unified language formed from hundreds of languages spoken throughout the Indonesian archipelago. Compared to other languages, which have a high density of native speakers, Indonesian is spoken as a mother tongue by only 7% of the population, and more than 195 million people speak it as a second language with varying degrees of proficiency. There are approximately 300 ethnic groups living throughout 17,508 islands, speaking 365 native languages or no less than 669 dialects (Tan, 2004). At home, people speak their own language, such as Javanese, Sundanese or Balinese, even though almost everybody has a good understanding of Indonesian as they learn it in school. Although the Indonesian language is infused with highly distinctive accents from different ethnic languages, there are many similarities in patterns across the archipelago. Modern Indonesian is derived from the literary of the Malay dialect. Thus, it is closely related to the Malay spoken in Malaysia, Singapore, Brunei, and some other areas. Unlike the Chinese language, it is not a tonal language. Compared with European languages, Indonesian has a strikingly small use of gendered words. Plurals are often expressed by means of word repetition. It is also a member of the agglutinative language family, meaning that it has a complex range of prefixes and suffixes, which are attached to base words. Consequently, a word can become very long. More details on Indonesian characteristics can be found in (Sakti et al., 2004). 3 Indonesian Phoneme Set The Indonesian phoneme set is defined based on Indonesian grammar described in (Alwi et al., 2003). A full phoneme set contains 33 phoneme symbols in total, which consists of 10 vowels (including diphthongs), 22 consonants, and one silent symbol. The vowel articulation pattern of the Indonesian language, which indicates the first two resonances of the vocal tract, F1 (height) and F2 (backness), is shown in Fig. 2.