A method of producing at least one possible sequence of vocal tract
resonance (VTR) for a fixed sequence of phonetic units, and producing the
acoustic observation probability by integrating over such distributions
is provided. The method includes identifying a sequence of target
distributions for a VTR sequence corresponding to a phone sequence with a
given segmentation. The sequence of target distributions is applied to a
finite impulse response filter to produce distributions for possible VTR
trajectories. Then these distributions are applied to a linearized
nonlinear function to produce the acoustic observation probability for
the given sequence of phonetic units. This acoustic observation
probability is used for phonetic recognition.