Source driven variable bit rate prototype interpolation coding

Current developments in high quality, low bit rate speech coders are focused at bit rates in the region of 2.4 kbps and below. This paper presents a source driven variable bit rate coding scheme which operates in conjunction with a prototype interpolation coder (PIC). The proposed SD-VBRC-PIC coder explores effectively the residual redundancy that can be found in the evolution with time trajectories of the PIC model parameters, using a variable synthesis frame size technique. Furthermore, this approach is generic and VBRC can be applied to other prototype interpolation coding systems. Computer simulation experiments show that on average up to a maximum of 30% bit rate savings can be achieved for the same recovered speech quality, as compared to the fixed bit rate of the PIC system under consideration.