# Tibetan Speech Synthesis Based on Pre-Trained Mixture Alignment FastSpeech2
## 2 Model Architecture
### Tibetan Text Preprocessing  
The majority of contemporary Tibetan speech synthesis models employing deep neural networks utilize Tibetan phonemes as their foundational synthesis units. Converting Tibetan text into phonemes necessitates a comprehensive and precise syllable lexicon. Characterized by its uniqueness and complexity, the Tibetan writing system possesses a rich character structure. This lexicon encompasses a myriad of potential syllable combinations, each corresponding to a distinct phonological unit. Constructing such a syllabic lexicon requires profound expertise in Tibetan linguistics and can be challenging due to the complexity and size of the lexicon. Additionally, even with a precise syllabic dictionary, there may still be potential noise.  
To address these challenges and simplify the process, this paper opts to use Wylie transcription to convert Tibetan characters into Latin letters. Wylie transcription is a widely recognized system that provides a standardized approach to transliterating Tibetan script into Latin characters. This system maps Tibetan syllables to specific Latin letter combinations based on their phonetic properties, thus creating a one-to-one correspondence between Tibetan sounds and Latin representations. In the Wylie transcription system, the process of converting Tibetan characters into Latin letters includes the following rules:  
* Tibetan vowels and consonants are transcribed into specific Latin letters or combinations, ensuring consistency across different Tibetan words and phrases.
* Tibetan syllables typically include a root letter along with possible prefixes, superscripts, subscripts, and postfixes. The Wylie transcription system provides specific rules for these components.
* Special symbols and tonal marks in Tibetan are represented by specific Latin characters in the Wylie transcription system to reduce ambiguity and preserve phonetic detail. Additionally, some syllable combinations undergo phonological changes in specific contexts, and the Wylie system typically transcribes the original characters directly.  
Figure 1: The overall architecture of the model. The Tibetan text in the figure, which appears in the text preprocessing section, translates to ‘Auspicious and Prosperous’.  
This method reduces the complexity and potential noise associated with managing a comprehensive syllabic lexicon, thereby providing a more efficient solution for synthesizing Tibetan speech. The use of Wylie transcription helps address lexical disparities by offering a consistent transliteration approach, which is crucial for accurate grapheme conversion.  
In practical applications, the process of transcribing Tibetan characters into Latin letters involves several steps. Initially, Tibetan text is processed by removing unnecessary spaces and punctuation marks and segmenting them into individual syllables. Each Tibetan letter is subsequently matched to its corresponding Latin letter according to Wylie transcription rules, involving the identification and conversion of root letters, prefixes, superscripts, subscripts, and suffixes. Finally, these transcribed components are combined to generate the complete Wylie transcription string. Notably, the symbol \"\(|\)\" is omitted at the end of sentences, and the symbol \"\(\cdot\)\" is transcribed as a space, simplifying the treatment of special symbols. Figure 2 displays the Latin letter representations of certain Tibetan characters transcribed via Wylie, visually illustrating these steps and providing a clear and standardized Latin representation of Tibetan sentences while preserving the original letter order.