Study And Optimization Of SPEEX Wideband Speech Codec In Electronic Tour Guide System

With the rapid development of tourism, the electronic tour guide system has been advanced and becomes a research hotspot. The speech codec applied in a wireless electronic tour guide system should be low bit-rate, robust to data lost and suitable for wireless data transmission. SPEEX is an open-source CELP codec satisfying the above requirement, thus it's suitable for wireless electronic tour guide system.On analysis of some important algorithms of CELP, a comprehensive study on the algorithm, the characteristic, the encoding modes and the structure of SPEEX have been completed. Then the algorithm of constructing a new perceptual weighting filter in SPEEX with the psychoacoustic model is optimized by designing new schemes. In the proposed algorithms, LSP coefficients or filter coefficients are interpolated to reduce its complexity. The result of the experiment shows that the average coding time has been decreased by 18% and 53% respectively, with little impact on the speech quality.The SPEEX decoder has been non-distorted optimized base on Freescale 56800E DSP. We reassign the decoder's stack and the memory, reconstruct the c code and reduce the redundancies.According to the way CodeWarrior compiles, we optimize c code and the algorithm of decoding bits from the bit stream. Then the assembly code of key modules is rewrote by using the special DSP instructions. Furthermore, we realize the SPEEX decoder on the receiver of the electronic tour guide system.Compared with reference code, the optimization result reduces code size, data size and heap size by 49.5%, 60.23% and 95.92%. reduces the average instructions and machine cycles spent on decoding one speech frame by 60.82% and 66.13%. The complexity of SPEEX decoder has been decrease from 31.64MIPS to 12.40 MIPS now, Thus, the decoding speed improved by 2.55times.