Research And Implementation Of G.718 Wideband Speech And Audio Coding Algorithm

With the rapid development of mobile and network communication technology, the speech compression coding technology is developing in the direction of the wideband, variable bit rate and embedded. In June, 2008, ITU-T proposed a new wideband speech and audio codec standard G.718 which is cater to the trend of the development of speech coding algorithm. The G.718 which was widely used in audio/video conference, 3G, 4G, multimedia stream, etc. has a flexible coding structure and high synthetic speech quality, it also has connectivity ability between network and wireless communication system.This topic thorough comprehend the G.718 speech coding standards mainly focused on its codec principle and structure characteristics of L1~L5 layers. Analysis of the key technologies which the G.718 core layer L1 and ACELP enhancement layer L2 used, such as preprocessing, signal classification, and ACELP, etc. Comparison of the differences and the similarities about the core layer coding between the G.718 and the other wideband speech codec. Studied the G.718 used the transform domain of coding technology in L3, L4, L5, while under the whole frequency signal input, the Algebraic Vector Quantization technique for speech signal, the Band-Selective Shape-Gain Coding and the Factorial Pulse Coding for audio signals. Introduces a fast algorithm based on FFT MDCT which is suitable for application by DSP.Because of the G.718 algorithm was complex, and the standard C code provided by ITU-T mainly focus on describe the algorithm, lead to execution efficiency was extremely low and hard to real-time implementation. This topic through analysis of each function in the standard C code, the relationship and the complexity of each module, present a whole assembly realization of G.718 speech codec based on DSP which combining with the characteristics of DSP C55 x assembly language to made the coding scheme of each module. Write the G.718 codec while maintaining the overall framework of the standard C code. Using the loop body optimization, parallel instructions optimization methods to optimization the assembly code for further improve the execution efficiency. In order to test the assembly of G.718 codec speech quality, this topic design the G.718 real-time testing system based on TMS320VC5505 EVM, after WB_PESQ objective evaluation, the G.718 codec achieve the requirements of real-time communication.