Proceedings of the 6th WSEAS International Conference on Signal Processing, Robotics and Automation, Corfu Island, Greece, February 16-19, 2007 77 A Romanian Syllable-Based Text-To-Speech System OVIDIU BUZA, GAVRIL TODEREAN Department of Telecommunications Technical University of Cluj-Napoca 26 – 28 G. Baritiu Str., 400027, Cluj-Napoca ROMANIA Abstract: - In this article we present the way we have built a syllable-based TTS system for Romanian. The system contains: a text analyser capable to separate syllables from input text and detect accentuation, a vocal database with recorded syllables, a unit matching module and a synthesizer. The analyser was built using a LEX generator by mean of two sets of phonetic rules. Vocal database was generated through an automated wave segmentation procedure. Key-Words: - syllable text-to-speech system, rule-driven text analyser, automatic segmentation 1 Introduction Also, Romanian language contains a relative Concatenation of waveforms represents a method small number of syllables, so we have obtained a more and more used in our days because of high reduced size of vocal database. level of naturalness in produced speech. Corpus- Our text-to-speech system consists of ([7]): based methods are among best approaches, but - a text analysis module that brings input text and they need great efforts for database maintaining. produces basic units, that in our approach are Syllable-base methods can be an alternative, as syllables, and prosody data, which mean the they need a limited units database. Using of information about how words are accentuated; syllables in synthesis also leads to a good level of - a unit matching module that generates acoustic speech naturalness and low concatenation error units sequence according to the linguistic units rate because of small number of concatenation detected from the input and prosody data; points inside the synthesized text. - a speech synthesis module that generates speech This article presents an original approach for based on the acoustic units sequences. constructing a syllable-based TTS system for Romanian. The syllable approach is very The particular aspects of our work are: appropriate in our case, because Romanian spoken - using of linguistic and phonetic rules based of language contains a big number of opened vowels which we have done text analysis and obtained that gives a constant rhythm of speech and similar appropriate units and prosody data; manner of accentuating words. - automatic generation of database from recorded sequences. Basic units Text Unit Text Synthesis Analysis Matching Prosody data Fig.1. Main functionalities of our Text-to-Speech system Proceedings of the 6th WSEAS International Conference on Signal Processing, Robotics and Automation, Corfu Island, Greece, February 16-19, 2007 78 First of all we have built a linguistic analyzer detection of syllables we had to design a set of module that is capable to split the input text into linguistic rules for splitting words into syllables, syllables. Next step was to determine accentuation inspired from Romanian syntax rules ([2], [3]). by mean of a phonetic analyzer. Then we have The principle used in detecting linguistic units automatically produced a database with PCM is illustrated in figure no. 2. Here we can see the coded syllables of Romanian language. Synthesis structure of text analyser that corresponds to four was done by concatenating acoustic units from modules designed for detection of units, prosody database and giving appropriate commands to the information and unit processing. computer’ sound blaster for voice generation. These modules are: - lexical analysis module for detection of basic units; 2 Text Analysis - phonetic analysis module for generating prosody First stage in text analysis is the detection of information; linguistic units: sentences, words and segmental - high level analysis module for detection of high- units, that in our approach are the word syllables. level units; Detection of sentences and words is done - processing shell for unit processing. based on punctuation and literal separators. For Sub Unit Processing Routines processing Shell Sintactical Sentences High Level Rules Analysis Words Text Lexical Phonetic Stress Analysis Syllables Analysis position Numbers Separators Lexical Phonetic Rules Rules Fig.2. Text analyser for syllable detection Processing shell accomplishes the unit characters, special characters and punctuation processing task and controls the subsequent marks. Using special lexical rules (that have been modules. The shell calls high-level analyser for presented in [8]), alphabetical characters are returning main syntactic units. High-level clustered as syllables, digits are clustered as analyser calls the lexical analyser for input text numbers and special characters and punctuation parsing and detection of basic units. Then marks are used in determining of word and phonetic analysis module is called for generating sentence boundaries. stress information. Phonetic analyser gets the syllables between Lexical analyser extracts text characters and two breaking characters and detects stress clusters them into basic units. We refer to the position, i.e. the accentuated syllable from detection of alphabetical characters, numerical corresponding word. Proceedings of the 6th WSEAS International Conference on Signal Processing, Robotics and Automation, Corfu Island, Greece, February 16-19, 2007 79 Then, high-level analyser takes the syllables, Text special characters and numbers provided by the C C C C C C C C C C lexical analyser, and also prosodic information, and constructs high-level units: words and sentences. Also basic sentence verification is done Digit Separator Alphanumeric here. Processing shell finally takes linguistic units provided from the previous levels and, based on some computing subroutines, classifies and stores Rules Rules Rules them in appropriate structures. From here synthesis module will construct the acoustic waves and will synthesize the text. Integer Real Sep 1 … Sep n Syllable 3 Lexical Analysis for Syllable Process separator Detection Process number Process syllable Lexical analyzer is called by the higher level modules for detection of basic lexical units: syllables, breaking characters and numbers. The Fig.3. Lexical analyser for syllable detection lexical analyzer is made by using LEX scanner generator [4]. LEX generates a lexical scanner starting from an input grammar that describes the 3.1 Specific actions of lexical analyser parsing rules. Grammar is written in BNF Specific actions inform high-level module about standard form and specifies character sequences matching of syllables, numbers and breaking that can be recognized from the input. These characters. Inside lexical parser three types of sequences refer to syllables, special characters, input response actions are defined as follows: separators and numbers. Also BNF grammar A. Process syllable – this is the action to be specifies the actions to be taken in the response of taken when a syllable is matched in specific input matching, actions that will be accomplished location of one word. by the processing shell subroutines. Special attention is taken when a syllable is The whole process realized by the lexical matched at the beginning of a word. In Romanian, analyzer is illustrated in figure no. 3. As we can different word decomposition rules apply when a see, input text is interpreted as a character string. character sequence occurs at the beginning or in At the beginning, current character is classified in the middle or the final part of a word. following categories: digit, special character or B. Process number – is the action to be separator, and alphanumeric character. Taking taken when a number is matched from the input. into account left and right context, current The number is identified as INTEGER or REAL character and the characters already parsed are type. In future stage, numbers will be translated in grouped to form a lexical unit: a syllable, a orthographic alphabetical form. number or a separator. Specific production rules C. Process separator - is the action for each category indicate the mode each lexical corresponding to a breaking character matching unit is formed and classified, and also realize a from the input. Breaking characters and subclasification of units (for numbers if they are punctuation marks are used for detecting word integer or real numbers, and for separators – the and sentence boundaries. type: word or sentence separator, affirmative, interrogative, imperative or special separator). 3.2 Syllable rules matching Once the unit type and subtype is identified, Regarding syllable rules matching process inside corresponding character sequence is stored and lexical analyser, two types of rule sets were made: transmitted to the high-level analyzer by mean of a basic set consisting of three general rules, and a specific actions, as they will be described in next large set of exception rules which statues the paragraph (Process syllable, Process number, exceptions from the basic set. Process separator). Proceedings of the 6th WSEAS International Conference on Signal Processing, Robotics and Automation, Corfu Island, Greece, February 16-19, 2007 80 (A) The basic set shows the general In Romanian stressed syllable can be one of decomposition rules for Romanian. First rule is last four syllables of the word: Sn, Sn-1, Sn-2 or Sn-3, that a syllable consists of a sequence of ( Sn is the last syllable). Most often, stress is