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Speech coding is being developed in balancing between reducing bitrate and decoding higher quality of audio.In fact,bitrate corresponds to bandwidth,so reducing bitrate is to compress bandwidth.In the recent decade,telephone and mobile communication develops rapidly,so bandwidth resource becomes more precious.Channel efficiency becomes a key factor, which expedite speech coding to develop continuously.It has already become an important criterion to judge quality of speech coding algorithms to obtain lower bitrate without reducing decoding quality of audio.The research in this article is about extreme low speed speech coding algorithm(Advanced Multi-Band Excitation,AMBE) based on multi-band excitation(MBE) speech coding.MBE,a high audio quality and low bitrate speech coding technique, was developed at MIT Lincoln Laboratory in 1988.IMBE,an improved algorithm of MBE,was adapted by INMARSAT and AUSAT satellite communication as speech coding standards.MBE was widely used in multiple areas,due to its excellent performance with bitrate lower than 4.8 kbps.AMBE,based on MBE,is an extension and improvement of standard MBE. The new AMBE,developed by Digital Voice Systems,Inc.(DVSI),has a bitrate lower than 2.4 kbps and uses A-B-S technique,voice activity detection(VAD),CNI,etc.The speech coding,being able to transfer high quality audio under extreme low bitrate,is proved to be better than CELP, RELP,MELP,ECELP,MP-MLQ,LPC-10 and other speech coding techniques.Firstly,in this article,parameter quantification coding method in AMBE was studied to achieve extreme low bitrate by keeping audio quality. The algorithm speed,audio quality of decoding and etc.were analyzed, by simulating AMBE speech coding.The speech coding in this article was proved to be useful,effective and have high extensibility and wide applicability.Secondly,the digital encrypted telephone system designed in this article is based on AMBE-2020TM vocoder chip,which boasts bright development of applications with its great advantage,because comprised with ordinary analog telephone,its output is as clear as the ordinary analog telephone at a low bitrate of 2.0 Kbps.
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