An-Najah Staff

This paper discusses the speech morphing process showing some limitations of using the directly obtained LPC and excitation parameters of speech. The algorithm here depends on changing the pitch of the source to match that of the target based on analyzing the speech signals to its basic components. Different experiments for changing the female to female, male to male, male to female and female to male speech were performed. Interesting results were obtained while dealing with children's speech. Difficulties of obtaining the pitch period were overcome but the obtained results have some diversity in the quality of performance even though the pitch has been changed correctly. The method for obtaining LPC and excitation used could be improved which could provide better results for this application.

Two iterative algorithms for pulse-based linear predictive (PB-LP) analysis are developed. At the kth step, one of the algorithms assumes that the pulse locations of k pulses are known and calculates the LP coefficients jointly with k pulse amplitudes. In contrast, the other algorithm assumes that the previous k-1 pulse amplitudes are known and jointly estimates the LP filter coefficients and the kth pulse amplitude. These algorithms are proposed for synthesis filter reoptimization in pulse-based LP coders, and their effectiveness in multipulse coding is demonstrated through several simulations

The conventional linear predictive analysis in pulse-based coders is replaced by the so-called source-combined linear predictive method to match the excitations considered in two steps: synthesis filter determination and excitation search. It differs from Atal's two-pass approach in that the synthesis filter is optimised jointly with the excitation prior to the ABS excitation search. However, it is a difficult task to obtain the optimum solution, and, thus, a suboptimal algorithm is developed. Initially, the algorithm starts with the covariance method and then corrects the synthesis filter using an estimate of the excitation. This is accomplished by using two coupled equations originally developed. The effectiveness of the approach in multipulse and regular pulse excited coders is demonstrated. Extensive simulation results, at several bit rates, with different excitations, are presented. Comparisons are made with the standard coder and the coder that employs Atal's approach. In all conditions, the proposed coder is found to give better results.