A 4.2 kb/s low-delay speech coder with modified CELP

In this letter, we propose a low-delay speech coder at 4.2 kb/s. In the proposed coder, we remove short-term prediction and use three-tap long term prediction to exploit the speech redundancy. A "dual-decision" pitch estimation algorithm and an adaptive sinusoidal excitation codebook are introduced to improve the performance of the proposed coder. The synthesized speech of this coder has comparable quality to that of conventional CELP coders at similar bit rates, while it has a coding delay of only 5 ms.