Editing Hidden Markov Models in Speech Synthesis (section)

==== Unit Selection Synthesis ====
During the 1990s, unit selection synthesis, also known as corpus-based concatenative synthesis, emerged, driven by the growing power of computer technology and the increasing availability of speech and linguistic resources <ref>Hunt, A. J., & Black, A. W. (1996). Unit selection in a concatenative speech synthesis system using a large speech database. ''1996 IEEE International Conference on Acoustics, Speech, and Signal Processing Conference Proceedings'', ''1'', 373–376. <nowiki>https://doi.org/10.1109/ICASSP.1996.541110</nowiki></ref>. 

Unit selection synthesis addresses issues associated with prosodic modifications in concatenative synthesis. It stores multiple instances of each unit with varying prosodies in the unit inventory, allowing for better matching to the target prosody. An algorithm selects the units that best match the target specification based on minimizing target cost and join cost functions.

However, Unit selection synthesis has limitations in terms of expressiveness, customization, and prosody control due to its reliance on recorded speech units and extensive databases <ref>Tokuda, K., Nankaku, Y., Toda, T., Zen, H., Yamagishi, J., & Oura, K. (2013). Speech Synthesis Based on Hidden Markov Models. ''Proceedings of the IEEE'', ''101''(5), 1234–1252. <nowiki>https://doi.org/10.1109/JPROC.2013.2251852</nowiki></ref>.