Investigation of the spectral envelope estimation vocoder and improved pitch estimation based on the sinusoidal speech model

In most low rate speech coders the quality of the synthesized speech depends greatly on the performance of the spectral coding stage, in which the spectral envelope is encoded. The spectral envelope estimation vocoder (SEEVOC) is a successful spectral envelope coding method, and also plays an important role in speech coding based on the sinusoidal model. This paper investigates the properties and limitations of the SEEVOC algorithm, which requires an estimate of the coarse pitch. Our analysis of the effect of inaccurate coarse pitch gives a new insight into the spectral envelope estimator, and shows that it is important to start with a reasonably accurate coarse pitch value. Also, we optimize and generalize the properties of the SEEVOC algorithm and propose a new method to improve pitch estimation based on the sinusoidal speech model