The Optimal Codebook Algorithm Research Of AMR-WB Speech Codec

In the public telephone networks, The AMR(Adaptive Multi-rate, AMR)speech codec used in GSM and WCDMA system is a multirate narrowband speech codec. For the limited bandwidth, the narrowband AMR speech codec can't satisfy people's needs to high quality speech services. With the rapid development of the digital networks and audio-visual technique application, people are in the pursuit of face-to-face communication. Conclusively the research of the wideband code is necessary.In order to meet the requirement in high quality speech services, 3GPP/ETSI proposed the adaptive multi-rate wideband speech codec.After that, the AMR-WB codec was selected by ITU-T in the standardization activity for wideband speech coding around 16kbit/s. AMR-WB(Adaptive Multi-rate Wideband, AMR-WB) codec makes speech frequency extended to 7kHz and sample frequency extended to 16kHz, greatly breakthroughs the restriction of the bandwidth than the narrow band codec. Therefore, AMR-WB codec will ameliorate greatly in many aspects such as speech naturalness and musical processing. AMR-WB has the advantages of high speech quality, low average bit rate and strong adaptability. The adoption of AMR-WB by ITU-T is of significant importance for it is the speech code system adopted both by wireless and wire line service at first time, and will be used widely in wireless communication fields as well as wire line communication fields.This paper systemically analyzed the AMR-WB algorithm. Based on deep research of vector quantization, adaptive codebook search,fixed codebook search, high band process and the decoding principle, the AMR-WB algorithm was simulated. The standard speech files(16kHz,16bit) of TIMIT standard English speech database were selected to accomplish coding and decoding experiments, then tested the synthesized speech in subject auditory quality and object w-PESQ value. The result showed above the model of 12.65kbit/s, the waveform of synthesized speech is the same as that of input speech, and it had hardly to differentiate with original input speech in auditory, he w-PESQ values were more than 4.0. In the model of 6.60kbit/s and 8.85kbit/s, there were a little distortion in terms of waveform and auditory, and the w-PESQ values were above 3.5. They all reached the communication quality standard and the synthesized speech had the good naturalness and comfortable auditory property.For adaptive multi-rate wideband speech codec algorithm, the paper optimizaties vector quantization and the adaptive codebook search the adaptive codebook search and fixed book search. And improved algorithms encoding and decoding were tested by voice quality algorithm. Compared with the original wideband speech coding standard G.722.2(AMR-WB)algorithm, optimizated vector quantization algorithm and adaptive codebook search algorithm both can significantly reduce the computational complexity and speech coding time, so two kinds of codeword search algorithm is fast and effective coding method and has certain application value. Compared with original fixed book search algorithm, optimizated fixed book search algorithm can improve voice quality and has a certain reference value.