4 . aimed at the reduction of bit rate and the improvement of speech quality , a serial of speech coding schemes are studied in a gradual refinement way , and an integrated coding scheme at 1 . 5 - 2 . 4kbps is presented finally 围绕编码位率的降低和语音质量的提高,以逐步求精层层递进的方式研究了一系列压缩编码方案,并最终提出一个位率在1 . 5 2 . 4kbps的综合编码方案。