Speech coder with low complexity and optimized codebook

This paper describes a speech coder with low complexity and optimized codebook. A 13 Kb/s speech coder is used for upbanded IS-95, a personal communications system (PCS) standard. This speech coder is called Qualcomm code excited linear prediction (QCELP). QCELP coder uses the closed-loop search for all pitch delays in each pitch subframe. This pitch search requires much computation time. And the coder has two codebooks, each of which consists of 128 circular entries which are generated from a Gaussian source. This kind of circular Gaussian codebook reduces the storage complexity, but doesn't have the speech property. We used two-stage pitch analysis for complexity reduction and an optimized codebook, which has a speech property and a circular structure, for better quality in Korean speech. The improved coder shows better performance than that of the original QCELP coder in complexity and speech quality.