A speech coding algorithm based on predictive coding

Abstract

Summary form only given. A compression algorithm for high quality speech signal using predictive coding techniques is developed. Code-excited linear predictive coding (CELPC) is one of the key techniques to compress speech signal to a bit-rate around 4.8 Kbps. However, due to the heavy computational requirement in the CELPC and speech signals usually can be divided into two portions: namely the based-band and the high-band frequency range. A hybrid CELPC and voice excited linear predictive coding (VELPC) scheme is developed for speech coding to reduce the complexity of the original CELPC. In the algorithm, a speech signal is firstly divided into two portions, the based-band and high-band respectively, in frequency domain, and then the low portion is coded with CELPC and the high-band portion is coded with VELPC. The test experiments showed this new coder can produce synthesized speech with good quality at a better bit rates than the original CELPC. When using the coding methods for the base-band and the high-band signal, we must decide how to divide the speech signal into two portions. In choosing the bandwidth of the base-band signal, there is a trade-off between the coding quality and the bit rate. In our experiment, the bandwidth of the base-band signal is chosen as one fourth of that of the original speech. Subjective evaluation experiments were conducted to test the performance of the hybrid CELPC and VELPC technique. For speech signal sampled at 8 kHz, a bit rate of 4.0 kbps can be achieved with frame intervals of 23 ms. The experimental results showed that the quality of the synthesized speech using hybrid coding technique at the bit rate of 4.0 kbps was almost the same as that of the CELPC at the bit rate of 4.8 kbps.