The Study Of ILBC Voice Arithmetic And Its DSP Realization

Along with the develop of VoIP technique, VoIP is becoming to a hot domain. Some VoIP voice arithmetic such as G723.1,G729,GSM610,iLBC,SPEEX are paid attention by industry.One of this paper's task is the study of iLBC voice arithmetic.The iLBC arithmetic essentially is the code excited linear predictive coding, it is a development of CELP. The iLBC have dynamic codebook update, voice enhancing arithmetic and package lose conceal technique, all of this make it have a better capability. According to the dissimilarity of the network bandwidth, the iLBC provide the 20ms and 30ms two kinds of coding formats. When decoding, the iLBC make use of analysis and synthesize method, the operation quantity of decoding part is comparatively small, this make it come true that real time decoding in client end which have not so strong function.The processing for each data packet is independently of the other data packets, it is the ideal choice of data packet communications. Even if the IP packet loss or the delay phenomenon deteriorate, this codec voice quality will not drop too bad.The iLBC is a narrowband voice codec, using the entire 4 kHz band, and most of the standard low bit rate codec using only from 300Hz to 3400Hz band. This point has a obvious impact on voice quality.In addition, the spectrum of iLBC accurately simulate the characteristics of the original signal, it has a more clear voice than the standard low bit rate codec. The iLBC algorithm provide very good fixed bit rate encoding for data packet network, getting a very good balance between quality and bit rate.Compare with the previous low bit rate codec algorithm, the iLBC algorithm is larruping in the dynamic codebook selection and update based on the initial state, the long time predictive method of interframe independent based on the PLC packet loss concealment techniques and the strengthen of residuals voice using conditional optimization algorithm. These places are worth studying.In this paper, another main task is realization of iLBC voice arithmetic on DSP.In the DSP realization, the C language iLBC voice algorithm in rfc3951 documents given by IEFE organization is standard algorithm, the ADSP2181 chip made by Analog Device company is the core DSP chip, and then convert the C language iLBC to DSP, making the code in line with the rules of ADSP2181 chip.After the transformation completes, use the massive speech sequence to test the code, and under the guarantee of speech quality, optimize the code from the instruction set, addressing modes, storage modes, temporary variables and other aspects. When the actual telephone tests, select the palmmicro company's AR1688 chip telephone, its interior DSP chip compatible with the ADSP2181 chip orders, the function is complete, meets the VoIP pronunciation need now, becomes the hardware platform when the actual test.