This article describes a new approach to estimate F0 curves using B-spline and Spline models characterized by a knot sequence and associated control points The free parameters of the model are the number of knots and their location The free-knot placement, which is a NP-hard problem, is done using a global MLE (Maximum Likelihood Estimation) within a simulated-annealing strategy Experiments are conducted in a speech processing context on a 7000 syllables french corpus We estimate the two challenging models for increasing values of the number of free parameters We show that a B-spline model provides a slightly better improvement than the Spline model in terms of RMS error.