The vocal tract (the throat from the vocal cords to the lips) has certain
major resonant frequencies. These frequencies change as the configuration of
the vocal tract changes, like when we produce different vowel sounds. These
resonant peaks in the vocal tract transfer function (or frequency response) are
known as "formants".
It is by the formant positions that the ear is able to differentiate one speech sound from another. Here are a few examples of English vowels with their corresponding lowest three formants for an average male speaker. Vowel sounds are in bold type and all values are in Hertz.
The SoftVoice synthesizer simulates the human speech production mechanism using digital oscillators, noise sources, and filters (formant resonators) just like an electronic music synthesizer. Because of this, we have the same flexibility as a music synthesizer to create different voice "patches", or presets. SoftVoice TTS comes with 20 preset voices which can be modified by the programmer or user.
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