Editing Festival Speech Synthesis System (1997) (section)

== Key Innovations ==
Based on the historical context that mentioned above, we have acquired a basic understanding of the early speech synthesis systems as well as its limitations. Over the years, there has been a transition from a String Based Processing System to Systems based on MLDS. This has revealed a comprehensive picture about how [https://www.cstr.ed.ac.uk/projects/festival/ Festival] stood out from other contemporary speech synthesis systems. While the Delta System, which was based on the MLDS, had gain much reputation in this domain, its short comings were also noteworthy. The [[wikipedia:Linear_complex_structure|linear structure]] applied by the multi-layered systems can pose constrains on data management, as well as restrict the flexibility of data representation and ability to adapt to complex linguistic relationships and structures. <ref>Hertz, S. R. (1990). The Delta programming language: an integrated approach to nonlinear phonology, phonetics, and speech synthesis. ''Papers in laboratory phonology'', ''1'', 215-257.</ref> 

=== Flexibility of Multiple Structure ===
In contrast, Festival diverges significantly from MLDS-based systems in several aspects, which also emerged as key innovations for it. First of all, Festival liberates linguistic items form the constraints of linear lists, making the utilization of various graph structures happen, like trees, lists and other linguistic structure. This intersecting relations also contributes to saving on redundancy.

Furthermore, items within Festival can exist within multiple structures, leading to more efficient and adaptable representations. Significantly, Festival allows for the incorporation of elements in various structures, fostering the creation of more effective and flexible representations. This innovative strategy empowers Festival to overcome the constraints imposed by the linear framework of traditional MLDS-based systems, fundamentally transforming the field of linguistic data processing.<ref>Black, A. W. (1999). " The Festival Speech synthesis System," System documentation, Edition 1.4, for Festival Version 1.4. 0. ''<nowiki>http://www</nowiki>. cstr. ed. ac. uk/projects/festival/manual/festival_toc. html''.</ref>

=== New Method for Concatenate Synthesis ===
In terms of concatenate synthesis, except for the conventional approach of using a single-instance diphone-based method<ref>Beutnagel, M. C., & Conkie, A. (1999, September). Interaction of units in a unit selection database. In ''EUROSPEECH'' (Vol. 99, pp. 1063-1066).</ref> with an inventory comprising one recording of each diphone type, Festival's speech synthesis system introduced a novel "clunits" technique. This method involves an inventory of units recorded within natural sentences and employs a limited form of unit selection.<ref>Clark, R. A. J., Richmond, K., & King, S. (2007). Multisyn: Open-domain unit selection for the Festival speech synthesis system. ''Speech Communication'', ''49''(4), 317–330. <nowiki>https://doi.org/10.1016/j.specom.2007.01.014</nowiki></ref>

To be more specific, the fundamental strategy involves organizing units within a specific category, like a particular sound, based on considerations about the context of pronunciation and intonation. This categorization relies on questions related to linguistic elements, such as whether the unit appears at the end of a phrase or is stressed within a syllable. Then the Festival system constructs decision trees for each sound in the database, with each leaf representing a list of database units determined by the questions leading to that specific leaf. During the synthesis process, Festival utilizes the appropriate decision tree to identify the optimal cluster of potential units for each targeted specification. A search is then conducted to determine the most suitable path through the potential units, taking into account the distance of each unit from its cluster center and the cost associated with joining adjacent units.<ref>Black, A. W., & Taylor, P. A. (1997). ''Automatically clustering similar units for unit selection in speech synthesis.'' <nowiki>https://era.ed.ac.uk/handle/1842/1236</nowiki></ref>

This new technique can avoid the issue of estimating weights in a feature-based target distance measure while maintaining sensitivity to prosodic and phonetic distinctions. Additionally, it effectively manages variability in unit sparseness, with the tree-building algorithm initiating a cluster split only when significant variations are identifiable.

=== Multilingual Compatibility ===
Another innovation point of this system lies in its multilingual compatibility'''.''' Festival supports various languages and can also be adapted to different linguistic contexts. Festival comes with support for English (British and American accent), [[wikipedia:Welsh_language|Welsh]] and [[wikipedia:Spanish_language|Spanish]]. Voice packages are available for various other languages, including [[wikipedia:Spanish_language|Castellano]], [[wikipedia:Czech_language|Czech]], [[wikipedia:Finnish_language|Finnish]], [[wikipedia:Hindi_language|Hindi]], [[wikipedia:Italian_language|Italian]], [[wikipedia:Marathi_language|Marathi]], [[wikipedia:Polish_language|Polish,]] [[wikipedia:Russian_language|Russian]], and [[wikipedia:Telugu_language|Telugu]].<ref>Black, A., Taylor, P., Caley, R., Clark, R., Richmond, K., King, S., ... & Zen, H. (2001). The festival speech synthesis system, version 1.4. 2. ''Unpublished document available via <nowiki>http://www</nowiki>. cstr. ed. ac. uk/projects/festival. html'', ''6'', 365-377.</ref>