SYSTEM AND METHOD FOR PERFORMING PITCH ESTIMATION AND ERROR CHECKING ON LOW ESTIMATED PITCH VALUES IN A CORRELATION BASED PITCH ESTIMATOR

An improved vocoder system and method for estimating pitch in a speech waveform which more accurately disregards false pitch estimates resulting from secondary excitations. The vocoder system first performs a correlation calculation on a speech frame and generates an estimated pitch value. The present invention then compares the estimated or determined pitch with a threshold value to determine if the determined or estimated pitch has a suspiciously low pitch value. If so, the present invention performs error checking to disregard pitch estimates that are the result of the First Formant frequency's contribution to the pitch estimation process. The error checking involves examining the higher multiples of the determined pitch value to ascertain whether the determined pitch value might be incorrect. The present invention determines whether one or more higher multiples are missing, whether the higher multiples are related by a common factor, and whether adjacent multiples have missing peaks. The error checking also involves searching for missing or low correlation peaks in the neighborhood of missing higher multiples of the determined pitch. If the error checking indicates that the determined pitch is probably incorrect, then a new determination is made without the correlation peak corresponding to the rejected determined pitch. This provides a more accurate pitch estimation, thus enhancing voice storage quality. The present invention thus comprises an improved correlation method for estimating the pitch parameter which more accurately disregards false correlation peaks resulting from secondary excitations, including the contribution of the First Formant.