The device designed for people who suffer from vocal cord dysfunction will contribute to manufacturing voice prostheses with improved affective features.
For instance, for little girls who have lost their voices, the improved artificial voice device can produce age-appropriate voices, instead of the usual adult voice.
These advances in artificial voice production have been made possible by results achieved in a research project led by Professor Samuli Siltanen, part of the Academy of Finland's Computational Science Research Programme (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 - the mouth and the throat.
This so-called glottal inverse filtering of the speech signal requires a highly specialised form of computer calculation. With traditional techniques, inverse filtration is only possible for low-pitch male voices.
Women and children voices are trickier cases as the higher pitch comes too close in frequency to the lowest resonance of the vocal tract.
The novel inverse calculation method significantly improves glottal inverse filtering in these cases.
"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," explains 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.
