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Unformatted text preview: D R A F T Speech and Language Processing: An introduction to natural language processing, computational linguistics, and speech recognition. Daniel Jurafsky & James H. Martin. Copyright c circlecopyrt 2006, All rights reserved. Draft of June 30, 2007. Do not cite without permission. 8 SPEECH SYNTHESIS And computers are getting smarter all the time: Scientists tell us that soon they will be able to talk to us. (By they I mean comput- ers: I doubt scientists will ever be able to talk to us.) Dave Barry In Vienna in 1769, Wolfgang von Kempelen built for the Empress Maria Theresa the famous Mechanical Turk, a chess-playing automaton consisting of a wooden box filled with gears, and a robot mannequin sitting behind the box who played chess by moving pieces with his mechanical arm. The Turk toured Europe and the Americas for decades, defeating Napolean Bonaparte and even playing Charles Babbage. The Mechanical Turk might have been one of the early successes of artificial intelligence if it were not for the fact that it was, alas, a hoax, powered by a human chessplayer hidden inside the box. What is perhaps less well-known is that von Kempelen, an extraordinarily prolific inventor, also built between 1769 and 1790 what is definitely not a hoax: the first full-sentence speech synthesizer. His device consisted of a bellows to simulate the lungs, a rubber mouthpiece and a nose aperature, a reed to simulate the vocal folds, various whistles for each of the fricatives. and a small auxiliary bellows to provide the puff of air for plosives. By moving levers with both hands, opening and closing various openings, and adjusting the flexible leather vocal tract, different consonants and vowels could be produced. More than two centuries later, we no longer build our speech synthesizers out of wood, leather, and rubber, nor do we need trained human operators. The modern task of speech synthesis , also called text-to-speech or TTS , is to produce speech (acoustic SPEECH SYNTHESIS TEXT-TO-SPEECH TTS waveforms) from text input. Modern speech synthesis has a wide variety of applications. Synthesizers are used, together with speech recognizers, in telephone-based conversational agents that con- duct dialogues with people (see Ch. 23). Synthesizer are also important in non- conversational applications that speak to people, such as in devices that read out loud for the blind, or in video games or childrens toys. Finally, speech synthesis can be used to speak for sufferers of neurological disorders, such as astrophysicist Steven Hawking who, having lost the use of his voice due to ALS, speaks by typing to a speech synthe- D R A F T 2 Chapter 8. Speech Synthesis sizer and having the synthesizer speak out the words. State of the art systems in speech synthesis can achieve remarkably natural speech for a very wide variety of input situa- tions, although even the best systems still tend to sound wooden and are limited in the voices they use....
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