Voice Simulation: Factors Affecting Quality And Naturalness

In this paper we describe a f lexib le analysls-synthesls system which can be used for a number of studies In speech research. The maln objective Is to have a synthesis system whose characteristics can be controlled through a set of parameters to realize any desired voice characteristics. The basic synthesis scheme consists of two steps: Generation of an excitation signal from pitch and galn contours and excitation of the linear system model described by linear prediction coefficients, We show that a number of basic studies such as time expansion/ compression, pitch modif icat ions and spectral expansion/compression can be made to study the e f fec t of these parameters on the qua l i ty of synthetic speech. A systematic study is made to determine factors responsible for unnaturalness tn synthetic speech. I t i s found that the shape of the g lo t ta l pulse determines the qua l i ty to a large extent. We have also made some studies to determine factors responsible for loss of I n t e l l i g i b i l i t y tn some segments of speech. A signal dependent analysts-synthesis scheme ts proposed to improve the i n t e l l i g i b i l i t y of dynamic sounds such as stops. A simple implementation of the signal dependent analysis is proposed.