Signal modification for voiced wideband speech coding and its application for IS-95 system

In CELP coding, signal modification is often employed to improve the pitch prediction at lowest bit rates. In this paper, a signal modification method for coding purely voiced wideband speech frames is introduced. The modification is performed frame and pitch synchronously preserving the original time scale at the end of each frame, which makes the method particularly convenient for variable bit rate coding. Special attention is paid to modify only the frames which are most suitable for the signal modification and low bit rate coding. The signal modification method is applied to a variable bit rate ACELP coder that satisfies IS-95/CDMA2000 rate-set II system requirements.