# Near-Optimal Active Learning for Multilingual Grapheme-to-Phoneme Conversion
## 2 Multilanguage Universal Phoneme Set  
Given that the International Phonetic Alphabet is intricate to transcribe and not widely recognized by computers, it is crucial to devise a computer-readable, universal phoneme set to develop pronunciation dictionaries and train multilingual acoustic models for use in multilingual speech processing systems. Nevertheless, a large phoneme set can increase the uncertainty of word annotation results and significantly augment the computational complexity of the decoding process. On the contrary, a small set of phonemes can reduce the accuracy of word annotations and impair the performance of speech processing systems. Therefore, an appropriate size phoneme set is crucial for developing an effective multilingual speech processing system. Articulatory features have been employed in multilingual and cross-lingual speech recognition [23; 24]. The inclusion of articulatory features aids in preserving language-specific phones during training, a critical aspect for promoting knowledge exchange in multilingual and cross-lingual speech recognition systems, especially for low-resource languages. Achieving successful multilingual and cross-lingual recognition entails fostering knowledge sharing during multilingual training and maximizing the transfer of knowledge from well-trained multilingual models to models for new languages. Traditionally, similar sounds across languages are merged into a unified multilingual phone set, as phones are regarded as the fundamental building blocks of speech. Nonetheless, it is widely acknowledged in phonology that phones can be decomposed into smaller, more elemental entities known as articulatory features, which can be shared across all languages [25]. These articulatory features represent phonological units through a collection of attributes, including voicing, high/low (indicating tongue position during vowels), roundness (pertaining to lip rounding), and continuity (distinguishing sounds such as vowels and fricatives from stops), among others. Table 1 provides a typical classification of generic pronunciation attributes based on two different methods, namely pronunciation manner (10 categories) and articulatory position (11 categories), in the current international mainstream phonology community. \"Pronunciation manner\" refers to the manner or method of articulating sounds in speech. Within the field of phonetics, pronunciation manner delineates how sounds are produced, encompassing aspects such as vocal cord vibration, the shaping of the oral cavity and pharynx, and the flow of airflow. Pronunciation manner has the capacity to influence the phonetic attributes of a given word, thereby aiding in the differentiation of diverse vocabulary or phonetic elements. For instance, a differentiating factor in the pronunciation manner between the English sounds \"p\" and \"b\" lies in the presence or absence of vocal cord vibration, thereby exerting an impact on the enunciation and semantic significance of words. \"Articulatory position\" refers to the specific location of different speech units (such as phonemes, consonants, or vowels) within the oral cavity during the production of speech. It involves the positioning, movement, and contact manner of speech organs such as the tongue, lips, and glottis. Articulatory position constitutes a significant determinant of acoustic distinctions among various speech sounds. Generic pronunciation attributes are a language-independently qualitative description with relatively few categories, and high accuracy can be achieved by recognizing these attributes. Although different phonological units exist in each language, many similar or \begin{table}
\begin{tabular}{c c} Pronunciation Manner & Vowel, Fricative, Nasal, Stop, Approximant, Continuant, Round, Tense, Voiced, Sil \\ Pronunciation position & Coronal, High, Dental, Glottal, Labial, Low, Mid, Retroflex, Velar, Anterior, Back \\  & \\ \end{tabular}
\end{table} 
Table 1: Generic pronunciation attribute table. identical phonological units can also be identified.