On the improvement of scalable MPEG-4 CELP at low bitrate

CELP (code-excited linear predictive), one of the speech coding techniques, is a part of the MPEG-4 standard. The distinct feature of the MPEG-4 CELP is that it has the bitrate and bandwidth scalability for different users with different network bandwidth. However, subjective experiments show that the scalable mechanism of the MPEG-4 CELP does not perform well at low core bitrates, e.g., 3.85 kbps. In this paper, we propose a method to generate the enhancement information that it better suited for low core bitrates. Experimental results show that the proposed approach has a better coded quality or such a situation.