Wolfgang von Kempelen's speaking machine is a manually operated speech synthesizer that began development in 1769, by Austro-Hungarian author and inventor Wolfgang von Kempelen. It was in this same year that he completed his far more famous contribution to history: The Turk, a chess-playing automaton, later revealed to be an elaborate hoax as it came to light that a person inside the automaton had secretly operated it. But while the Turk's construction was completed in six months, Kempelen's speaking machine occupied the next twenty years of his life. After two conceptual "dead ends" over the first five years of research, Kempelen's third direction ultimately led him to the design he felt comfortable deeming "final": a functional representational model of the human vocal tract.
First design Kempelen's first experiment with speech synthesis involved only the most rudimentary elements of the vocal tract necessary to produce speech-like sounds. A kitchen bellows, used to stoke fires in wood-burning stoves, was invoked as a set of lungs to supply the airflow. A reed extracted from a common bagpipe was implemented as the glottis, the source of the raw fundamental sound in the vocal tract. The bell of a clarinet made for a sufficient mouth, despite its rigid form. This basic model was able to produce simple vowel sounds only, though some additional articulation was possible by positioning one's hand at the bell opening to obstruct airflow. The physical hardware for constructing the nasals, plosives and fricatives that most consonants require was not present, however. Kempelen, like many other early pioneers of phonetics, misunderstood the source of the perceived "higher frequencies" of certain sounds as a function of the glottis, rather than as the function of the formants of the entire vocal tract, so he abandoned his single-reed design for a multiple-reed approach.
Second design The second design involved a console, similar to that of a musical organ of the period, in which the operator manned a set of keys, one for each letter. The sounds were produced by a common bellows that fed air through various pipes with the appropriate shapes and obstructions needed to produce that letter. Through experimentation, he came to find that the reed's resonant length was not crucial to the creation of the high-frequency components of certain vowels and fricatives, so he tuned them all to be the same pitch for the sake of consistency between letters. While not all letters were represented at this point, Kempelen had developed the technology required to produce most vowels and several consonants, including the plosive /p/, and the nasal /m/, and thus was in a position to begin forming syllables and short words. However, this immediately led to the primary flaw of his second design: the parallel nature of the multiple reeds allowed for more than one letter to be sounded at a time. And in the process of building syllables and words, the sonic “overlap” (now referred to as co-articulation) rendered sounds very uncharacteristic of human speech, undermining the intention of the design altogether. Kempelen comments: “In order to continue my experiments it was necessary, above all, that I should have a perfect knowledge of what I wanted to imitate. I had to make a formal study of speech and continually consult nature as I conducted my experiments. In this way my talking machine and my theory concerning speech made equal progress, the one serving as guide to the other.” "It was possible, following the methods I'd been using, to invent separate letters, but never to combine them to form syllables, and that it was absolutely necessary to follow nature which has only one glottis and one mouth, through which every sound emerges and which gives a unity to them." Thus, Kempelen began work on his third, and ultimately final design, which itself was in many ways a "close-as-possible" representation of the physiology of the vocal tract.
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