What happens when a person pronounces a vowel is that the overtone-rich vocal cord sound sets off all sorts of resonances in the mouth, nose and throat, whose frequency depends mostly on the shape of the mouth and position of the tongue. The characteristic sound of each vowel is created by formants - ranges of frequencies emphasised by the mouth and throat creating resonant cavities which pick out harmonics from the basic sound of the vocal cords. The most important frequencies for formants in German vowel sounds is shown in fig. 4 . fig. In the patch in fig.
Pitch is controlled by a keyboard.
The resonance of both of the band-pass filters should be set quite high. Another source for discovering the formant frequency range of English language vowel sounds is Allen Strange's book Electronic Music. If you're trying out the patch in fig. 5, then just use the first two frequency settings in each set of three. You can, if you want, alter the response of each individual filter , so that it is 12 db low-pass.