A new device which may help people who have lost their voices speak again is being developed by researchers.
For little girls who have lost their voices, for instance, the improved prostheses can produce age-appropriate voices, instead of the usual voice of an adult male.
These advances in artificial voice production have been made possible by results achieved in a research project led by Samuli Siltanen, professor at the Academy of Finland's Computational Science Research Program (LASTU).
One of the fundamental problems of speech signal analysis is to find the vocal cord excitation signal from a digitally recorded speech sound and to determine the shape of the vocal tract, i.e., the mouth and the throat, according to a Finland statement.
Women's and children's voices are trickier cases as the higher pitch comes too close in frequency to the lowest resonance of the vocal tract.
"Most speech sounds are a result of a specific process. The air flowing between the vocal folds makes them vibrate. This vibration, if we could hear it, would produce a weird buzzing sound. However, as it moves through the vocal tract, that buzz is transformed into some familiar vowel," explained Siltanen.
Singing, says Siltanen, is a perfect example of this interplay between the vocal cord response and the vocal tract. "When we sing the vowel 'a' in different pitches, our vocal tracts remain unchanged but the frequency of the vocal cord excitation changes.
"On the other hand, we can also sing different vowels in the same pitch, whereby the shape of the tract changes and the excitation stays the same," Siltanen said.