  The articulatory-acoustic relationship is many-to-one and non linear and this
is a great limitation for studying speech production. A simplification is
proposed to set a bijection between the vowel space (f1, f2) and the parametric
space of different vocal tract models. The generic area function model is based
on mixtures of cosines allowing the generation of main vowels with two
formulas. Then the mixture function is transformed into a coordination function
able to deal with articulatory parameters. This is shown that the coordination
function acts similarly with the Fant's model and with the 4-Tube DRM derived
from the generic model.
