White suspected that if he built digital vocal chords (stimulated by columns of mathematically simulated air) the system would achieve naturalism. The first results were a bit like the squeaker out of a dog toy, he said, which wasnt surprising: blow through the mouthpiece of a clarinet without the instrument, and the effect is similar. White then added a digital version of the pharynx, which sits behind the mouth and nasal cavity; it served as a resonator, amplifying sounds produced by the vocal chords, but also altering their texture. The squeaks became elongated. He called this the systems trumpety-chicken-duck-whale-car-horn phase. By the end of January, several weeks after he had started programming, he added a digital mouththe final component necessary for a rudimentary virtual vocal tract. Then he set about giving his creation a voice.
Every vowel is defined by a narrow band of frequencies, known as a formant, which are created by the vocal tract as a wholethe way sound resonates throughout all its parts. White found a paper from 1962, titled A Study of Formants of the Pure Vowels of British English. The paper, based on recordings of twenty-five male subjects, contained a table of the relevant data. Late one night, alone in his Edinburgh studio, he copied the values for a vowel labeled /a/ hard and plugged them into his system. The digital resonance that White had createdwith vocal chords, pharynx, and mouth all affecting each othercaused the utterance to take on human character, and the result was a blood-curdling scream.
