Closed Loop Dynamic Bit Allocation for Excitation Parameters in Analysis-by-Synthesis Speech Codec

A method for dynamically allocating bits for the adaptive and fixed codebook of an analysis-by-synthesis speech codec is proposed. The bit allocation is based on the closed loop weighted mean squared error. The different bit allocations identify various codebook configurations used by the adaptive and fixed codebooks of the codec. Unlike open loop approaches where the decision on a codebook configuration is made once per frame, in the closed loop approach the decision on which codebook configuration should be used is made in each subframe. A variable length code is used for coding the codebook configuration. The factorial packing codebook is used as the fixed codebook. The technique is a part of 8.5 kbps mode of EVRC-WB speech coding standard.