Algorithms for grapheme-phoneme translation for English and French: applications for database searches and speech synthesis

• Authors: Michel Divay;Anthony J. Vitale
• Venue: Computational Linguistics
• Year: 1997

Letter-to-sound rules, also known as grapheme-to-phoneme rules, are important computational tools and have been used for a variety of purposes including word or name lookups for database searches and speech synthesis.These rules are especially useful when integrated into database searches on names and addresses, since they can complement orthographic search algorithms that make use of permutation, deletion, and insertion by allowing for a comparison with the phonetic equivalent. In databases, phonetics can help retrieve a word or a proper name without the user needing to know the correct spelling. A phonetic index is built with the vocabulary of the application. This could be an entire dictionary, or a list of proper names. The searched word is then converted into phonetics and retrieved with its information, if the word is in the phonetic index. This phonetic lookup can be used to retrieve a misspelled word in a dictionary or a database, or in a text editor to suggest corrections.Such rules are also necessary to formalize grapheme-phoneme correspondences in speech synthesis architecture. In text-to-speech systems, these rules are typically used to create phonemes from computer text. These phonemic symbols, in turn, are used to feed lower-level phonetic modules (such as timing, intonation, vowel formant trajectories, etc.) which, in turn, feed a vocal tract model and finally output a waveform and, via a digital-analogue converter, synthesized speech. Such rules are a necessary and integral part of a text-to-speech system since a database lookup (dictionary search) is not sufficient to handle derived forms, new words, nonce forms, proper nouns, low-frequency technical jargon, and the like; such forms typically are not included in the database. And while the use of a dictionary is more important now that denser and faster memory is available to smaller systems, letter-to-sound still plays a crucial and central role in speech synthesis technology.Grapheme-to-phoneme technology is also useful in speech recognition, as a way of generating pronunciations for new words that may be available in grapheme form, or for naive users to add new words more easily. In that case, the system must generate the multiple variations of the word.While there are different problems in languages that use non-alphabetic writing systems (syllabaries, as in Japanese, or logographic systems, as in Chinese) (DeFrancis 1984), all alphabetic systems have a structured set of correspondences. These range from the trivial in languages like Spanish or Swahili, to extremely complex in languages such as English and French. This paper will outline some of the previous attempts to construct such rule sets and will describe new and successful approaches to the construction of letter-to-sound rules for English and French.